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# Aptitude - Problems on Trains - Discussion

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"In the middle of difficulty lies opportunity."
- Albert Einstein
2.

A train 125 m long passes a man, running at 5 km/hr in the same direction in which the train is going, in 10 seconds. The speed of the train is:

 [A]. 45 km/hr [B]. 50 km/hr [C]. 54 km/hr [D]. 55 km/hr

Explanation:

 Speed of the train relative to man = 125 m/sec 10

 = 25 m/sec. 2

 = 25 x 18 km/hr 2 5

= 45 km/hr.

Let the speed of the train be x km/hr. Then, relative speed = (x - 5) km/hr.

x - 5 = 45         x = 50 km/hr.

 Swati said: (Wed, Jul 7, 2010 09:44:16 AM) Why is it divided by 18/5?

 Jothi said: (Mon, Jul 12, 2010 12:13:56 PM) Please explain to sutract -5 but ans is 50.

 M.Saravanan said: (Wed, Jul 14, 2010 01:12:26 AM) Please explain 18/5.

 Shwetha A V said: (Fri, Jul 16, 2010 01:56:20 PM) 60*60/1000=18/5

 Saji said: (Mon, Jul 19, 2010 01:59:01 AM) 18/5 is to convert m/s to km/hr

 Ankita said: (Tue, Jul 20, 2010 07:47:39 AM) Why its substracted?

 Gowtham said: (Thu, Jul 22, 2010 02:25:20 AM) Hey why we findind relative speed??? They asking only speed na????

 Vijayagopal said: (Mon, Jul 26, 2010 04:36:15 AM) Why 125/10 the 10 is divided 125 please explain it.

 Rahul said: (Wed, Jul 28, 2010 03:29:43 PM) @gowtham It would be only speed if the man(REFERENCE POINT) was stationary and only the train was moving. Here as both trian and REFERENCE POINT(man) are moving relative motion comes into picture.

 Rahul said: (Wed, Jul 28, 2010 03:40:23 PM) @ankita when a man moves in the direction of train, the train speed is decreased by his own speed. If he moves in the opposite directon he finds the train speed to be much greater. So when is moving in the same direction his speed must be subtracted from that of train speed. If he moves in the opposite direction to that of train, then his speed must be added to the train speed. moving in same directon: SUBTRACT moving in opposite directon: ADD

 Rahul said: (Wed, Jul 28, 2010 03:50:33 PM) @ vijayagopal here both man and train are moving in the same direction and the train crosses the man in 10 seconds. speed = distance(or length)/time. As both man and train are moving, relative motion comes into picture. therefore: relative speed= (length of the train)/(time taken by the train to cross the man who is in motion) relative speed= 125/10

 N Ramesh Chandra said: (Fri, Aug 6, 2010 09:57:41 AM) Hai Madhu N Swathi, ****When two bodies say x km/hr and y km/hr are moving in the same direction then their relative speed is (x-y) km/hr ****When we want to convert km/hr in to m/s we multiply with 5/18. *** Let the speed of the train be x kmph Speed of the train relative to man(x-5)kmph (x-5)*5/18 now as we know that Distance/speed=time now,speed is (x-5)*5/18; distance is 125m; time is 10 sec; now u vl get the answer ***********

 Thilaga said: (Fri, Aug 13, 2010 05:52:39 AM) Nice explanation.Thanks.

 Umair Chudhary said: (Sat, Aug 21, 2010 01:06:49 AM) If someone feel difficult to understand 5/18 i.e; m/s To convert kmph to mps 1000/60*60 m/s It is same thing.

 Sreenivas Reddy said: (Fri, Sep 3, 2010 05:27:51 AM) Yeah superb.

 Kamalakannan said: (Sun, Sep 5, 2010 04:03:55 AM) Answer = 45 km/hr is relative speed of the train. Now, you calculate (u-v). The Speed of the train 50 km/hr answer is correct.

 Antony said: (Wed, Sep 8, 2010 05:14:24 AM) Please explain 18/5.

 Dattatray said: (Wed, Sep 8, 2010 07:35:23 AM) 18/5 = 1 km/hr = 1000/3600 m/s = 10/36 m/s = 5/18 m/s.

 Sheela said: (Wed, Sep 8, 2010 10:45:53 AM) 1km=1000m. 1hour=3600sec. So to convert from km/hr to m/sec, we need to divide 3600/1000 i.e,. 1km/1hr=3600s/1000m which is equal to 18/5. If it was asked to convert m/s to km/hr then it would be 1000m/3600s= 5/18

 Saranya said: (Thu, Sep 9, 2010 01:12:49 AM) I could not understand this problem is there any way to understand this more easily.

 Abhishek said: (Fri, Sep 10, 2010 05:55:25 AM) Distance = time * speed 125 = 10 * speed distance/time = speed 125/10 = (25/2)m/s = speed ---------------------------------------------------------- Answer should be in km/hr so convert m/s km = 1000m and hr = 3600s m = km/1000 and s = hr/3600 m/s = (3600/1000)km/hr m/s = (18/5)km/hr ---------------------------------------------------------- The condition was speed = (25/2)m/s = (25/2)(18/5)km/hr = 45 km/hr The speed was relative to man so we have taken time in consideration of man -------------------------------------------------------- See further in in view answer. ----------------------------------------------------------

 Nagapriya said: (Fri, Sep 17, 2010 12:43:25 AM) Now I understand that,. Distance = Speed*Time. Time = Distance/Speed. Speed= Distance/Time. OK guys, very thanks to your teaching.

 Amit said: (Tue, Sep 21, 2010 02:36:36 PM) Can any one tell me why we have mulipled 25/2 to 18/5..why it should not be multiplied by 5/18 and also how ? x - 5 = 45 ....as I understand it should be 40 km/hr x = 50 km/hr. Because x=45. 45-5=40....hence anyone pls clarify.

 Srikanth Mirdati said: (Sat, Sep 25, 2010 07:01:58 AM) Could anyone please tell me how we get to 25/2 by dividing 125/10. I want to know how the division of 125/10 is done to get 25/2 an answer would be appreciated greatly.

 Shabana said: (Sat, Sep 25, 2010 11:57:06 AM) Hi, Really the explanation given by Dattatray & Rahul was superb. Thanks guys.

 Manoj Chauhan said: (Tue, Sep 28, 2010 03:34:53 AM) 125/10 = 12.5 3600/1000 = 36/10 (you should delete the last two zeros) 36/10 = 3.6 x = 12.5 * 3.6 So that x = 45 per hour right (this is relative speed of train) x = 45 (you add 5 km per hour for train speed because 45 is relative speed of train). Therefore x = 50 (the required answer).

 Nitesh Nandwana said: (Tue, Sep 28, 2010 08:47:53 AM) Hai Rahul, well explanation about relative speed and same and opposite directions. Good job keep it up.

 K.C.Yogannal said: (Tue, Oct 5, 2010 05:40:10 AM) @Vijayagopal. As speed =length/time they have done 125/10. Where 125 is the length and 10 is the time. Hope you understood.

 Atique said: (Mon, Oct 11, 2010 02:13:59 AM) Nice Explanation Guys. Thanks a Lot.

 Anitha said: (Wed, Oct 27, 2010 01:30:47 AM) Why 18/5 please tell me?

 Anitha Alavala said: (Wed, Oct 27, 2010 01:51:03 AM) See the answer for 18/5 is how? 1 km=1000m & 1hr=3600sec by this we get 1km/1hr = 5/18 m/sec.But the answer must be in km/hr....But 5/18 is in m/sec. we have to convert it to km/hr. 1 km = 1000m => m = 1 km/1000 hr/3600) = (1km/1000)*(3600/1hr) = 3600km/1000hr => 18/5 km/hr friends...its a perfect answer...have a look.

 San said: (Wed, Oct 27, 2010 11:57:01 PM) I cant understand relative speed formula ie) x-5 is this standard formula ?

 Sathish said: (Wed, Nov 3, 2010 01:32:46 PM) (x-5) is not a standard formula x is taken as speed of train and 5 is man's speed, to calculate train's speed from relative speed we subtract (x-5).

 Chakit said: (Tue, Nov 9, 2010 12:14:05 PM) x - 5 = 45 x= 45+5 x = 50 km/hr.

 Sanya said: (Wed, Nov 10, 2010 02:52:25 AM) relative speed when two movable things whose speeds x,y are moving in same direction is =X-Y, relative speed when two movable things whose speeds x,y are moving in OPPOSITE direction is =X+Y Its an standard formula

 Onam said: (Fri, Nov 19, 2010 07:39:32 AM) 5/18 is conversion of km/hr to m/s and 18/5 is conversion digit m/s to km/s

 Vijay Kumar Kuppani said: (Sun, Nov 21, 2010 08:50:24 AM) DONT WORRY FRIENDS ITS VERY SIMPLE instead of going for a new formula.we can simply get the answer by using the standard formula.i,e t=(a+b)/(u-v) u can see this formula from the general formulas of this exercise. where t-time taken by the train to cross the man=10 sec; a-length of the train=125meters; b=0(because the train is supposed to cross a person); u=speed of the train(you are supposed to find out); v=speed of the man who is running=5km/hr=5*(5/18)=25/18m/sec; by substituting the values in the above equation you can get the value..

 Nas said: (Sat, Dec 4, 2010 12:52:38 AM) Nice explanation friends. !

 Priyavel said: (Wed, Dec 8, 2010 07:28:00 AM) Both (train and man) moves in same direction so we subtract. Both moves in opposite direction means we add it. We convert m into km, sec into hour so we multiply 18/5.

 Jelli said: (Sat, Dec 11, 2010 07:13:08 AM) Thanks to all. I got many idea's to solve this problem.

 Kannips said: (Sun, Dec 12, 2010 12:47:14 AM) speed=distance/time.so speed=125/10.....25/2*18/5=45... the question is same direction=x-5=45 x=50

 Kumar said: (Sun, Dec 12, 2010 02:07:50 PM) Why 125 is divided by 10?

 Prithika said: (Sun, Dec 19, 2010 12:47:47 AM) @kumar cause speed=distance/time

 Raghu said: (Tue, Dec 21, 2010 05:01:43 AM) How it is 3600/1000. It will come as 1000/3600 only. Please explain.

 Saranya said: (Tue, Dec 21, 2010 10:52:51 AM) hai raghu, in the question man's speed is given in km/hr so we gonna convert train's speed to km/hr which is actually in m/s 1 m/s = 3600 km/1000 hr 125/10 m/s= (125/10)*(3600/1000)

 Tahira said: (Tue, Dec 21, 2010 11:43:59 AM) Hai fnds. Howz the 12.5 is converted into 25. Please explain.

 Mani said: (Thu, Dec 23, 2010 03:47:22 AM) Hi Tahira, You just cancel 125/10 using multiples of 5. 125/10=25/2=12.5.

 Rekha said: (Thu, Dec 23, 2010 04:41:19 AM) Ramesh chandran. CLEAR explanaTION. THANKS.

 Shanmuga Priya.Tex said: (Thu, Dec 30, 2010 10:59:24 PM) NICE EXPLANATION ABHISHEK.

 Ravi U S said: (Sat, Jan 1, 2011 01:22:45 AM) Hi friends,the problem is very simple.Think in this way.Assume that the man is not moving(standing like a pole),now findout the speed of the train using the data. LENGTH OF THE TRAIN=125m. TIME TAKEN BY THE TRAIN TO CROSS THE MAN(assume standing)=10sec w k t velocity=distance(length of the train)/time. v=(125/10)m/s v=(25/2)m/s convert m/s into km/hr v=(25/2)* (3600/1000) or (25/2)*(18/5) v=45 km/hr 45 km/hr is the train speed if the person is standig(not moving). But in the problem person is moving and that to he is moving in the same direction in which train going,so that's y add the speed of the man to the speed of the train then we will got the correct answer. speed of the train+speed of the man=45+5=50 km/hr.

 Murali said: (Sat, Jan 8, 2011 02:26:24 AM) hai!frinds,. in this above problem they given speed of the one object. we know that if the two objectives are move in the same direction then the formula is"(A-B)"(assume A is one objective and B is another objective).so,nw we know one objective speed(taken as B speed we know),that is subtutited in above. then s=(A-5).(here it is the speed of the train) 1.in the problem train(objective) speed is given in the form of seconds,so convert the seconds into the km/hr.because of the one objective speed is give in the form of km/hr and also answer is given in the form of km/hr. 2.while the conversion we have to follow the following, i)if we covert m/sec inti km/hr then multiplis with"8/15" ii)if we convert km/hr into the m/sec then multiplies with "15/8" 3.we know the formula for speed is "speed=Distance/Time"(s=D/T) s=125/10 m/sec [here 125 is the distance,and 10 is the speed of the objective] the conversion s=125/10*(18/5)km/hr =45. 4.in starting we initialse the speed(s)=A-5 then subtuted that speed in the above, A-5=45 A=50. therefore the speed of the train(another objective) is "A=50".

 Amol said: (Mon, Jan 10, 2011 12:04:42 PM) Hi Friend's Thanks for teaching it really works dude , 1km=1000m and 1hr =36000 then 5/18 m/sec it's simple. Thanks for that .........!

 Amit said: (Sat, Jan 22, 2011 02:54:04 AM) Hi friend's Hey ravi nice explanation.

 Manishkumar said: (Sun, Jan 23, 2011 03:50:14 AM) @ all apply logic don't simply go for routine speed of man is 5km/hr and in mt/sec is 1.39. so total distance covered by main in 10 sec is 13.9 m so total distance covered by train in 10 sec is 125+13.9=138.9 so total distance covered by train in 1 sec is 13.89m and if we convert this in km/hr i.e. 13.89*3600/1000= 50km/hr

 Ravi U S said: (Tue, Jan 25, 2011 04:52:00 AM) Thanks Amit

 Rajesh Motana said: (Sat, Feb 12, 2011 02:03:27 AM) Train moves with speed 125m/10 sec,.. So need to convert it as KM/ Hr ,..To convert 125m to KM we have to divide it with 1000 so it is 125/1000 and to convert 10 sec to hrs we have to divide it with 3600 so it is 10/3600. Then it becomes (125/1000)Km/(10/3600)hr. So we can change it to (125/1000)*(3600/10).. It is (5/40)*(360) = (360*5)/40 = 180/4 = 45 Km/Hr. .. Now we have got the speed in 1 Hour ie 45 Km.. As the man is travelling at 5 Km/Hr.. In that 1 Hr he already travelled 5 Km's.. So the train speed should be 45+5 Km's to cross that person in that 1 Hr.. Now answer is 50 Km/Hr.. I hope it is clear,... Take a paper a write exactly what i have given above,.. I am sure u guys will like it..

 Abhishek said: (Sun, Feb 13, 2011 04:01:48 AM) Can anyone find another way of solving this? Apart from relative speed?

 Jeevanantham said: (Fri, Feb 18, 2011 10:00:26 AM) How to relative 45 with man running speed. Please explain it any one.

 Vimal said: (Thu, Mar 3, 2011 11:16:14 AM) This is good Question i understand that, some friend disturb for 18/5. its simple its unit for km/hr. let see that1km=1000m & 1hr = 3600 second so 1000/3600 = 5/18 . And see that If we want to small unit convert in to big unit we have to divide & if we want to big unit convert in to small we have to multiply so here they dividing and write 18/5 ok so encourage your self my friend go ahead. VIMAL SONI & DUSHYANT SONI

 Vasuedvareddy said: (Mon, Mar 7, 2011 02:16:22 AM) @Vasudeva reddy 1km = 1000m =100,000cm 1 inch = 2.54cm 1 ft=12 inches = (12*2.54)cm 1km = 0.621371192 mile 1.609344 km = 1 mile

 Sarah said: (Thu, Mar 17, 2011 05:08:03 AM) Hi I can't understand friends. What is this x-5 ? Please anyone explain clearly.

 Suganthan.M said: (Mon, Mar 28, 2011 07:54:30 AM) We need the speed of the train we have only one clue about the train is 125m and 10s speed=distance/time (i.e)125/10= 12.5 m/s but we need the answer in km/hr so convert it 12.5*(18/5)=12.5*3.6 =45 km/hr almost we got it then about the direction, it is in same direction Now the speed of the train as x, because of same direction subtract it from x x-5=45 x=45+5 x=50km/hr

 Chetana said: (Fri, Apr 1, 2011 10:13:28 AM) Thanks frnd. I understand properly.

 Gowthami said: (Thu, Apr 21, 2011 01:46:32 AM) Nice explanation from you frnds but ravi said that we had add that relative speed, I can't understand from his point of view.

 Jitendra Prajapati said: (Wed, Apr 27, 2011 02:40:04 AM) Very good explanation by Suganthan.

 Meera said: (Fri, May 13, 2011 01:00:55 PM) Thanks mr. Suganthan. Its really very nice to understand thanks:) ) ).

 Shashank said: (Wed, May 25, 2011 12:05:23 PM) Hi. Please tell me why x-5 ?

 Binod Verma said: (Sun, May 29, 2011 02:24:59 PM) When two things are running in the same direction or opposite direction then we say that motion is in relative between them. So at first we find the relative motion and then find the speed of train. If someone want to find out speed of man that are given in the question.

 Dhandapani said: (Mon, May 30, 2011 11:05:56 AM) Simple you can multiply 5*10. 5-a man running 5km/hr and the train reached in 10 seconds. 5*10=50km/hr.

 Washeru said: (Sun, Jun 5, 2011 11:44:52 AM) Good expl. frm Rahuul

 Ragavan said: (Fri, Jun 10, 2011 11:13:45 AM) As from the problem. two contrain have to remember *If the man moving towards train. so that train pass the man faster then speed so add the distance. *If not move towards train. The train pass the man late.so minus the distance

 Arul said: (Thu, Jun 30, 2011 10:19:05 PM) Hey the quesion is about the speed of the train. jjust bcoz aman runs... will the speed of the train increase...? a little help here pls...

 Salahuddin said: (Mon, Jul 4, 2011 07:42:31 AM) To avoid confusion Simple convert the trains speed for 1 hr - metres/seconds, 125m/10 sec. So 125 * 6 * 60 / 10 * 6 * 60 = 45000 mtrs/ 3600 . So to convert it, divide by 1000, its 45 kms/hr. As the man running in the same direction at a speed of 5kms/hr add 45 + 5, if the person moves in opposite direction then subtract. Just logic guys

 Kaushik Rathod said: (Tue, Jul 5, 2011 05:22:27 AM) Answer in Another way :- Speed = 5*18/5 = 18 km/hr Time = 10 sec. X + 125 / 10 = 18 X + 125 = 180 X = 180-125 X=55 Now, Speed = X-5 So , Speed = 55 - 5 Speed = 50 km/hr

 Ajith said: (Mon, Jul 11, 2011 10:19:18 AM) So in the above problem let us consider that the speed of the person is 5 km\hr . Leave the 5 as it is and then convert the km\hr into m\s that means 1 km=1000m and 60min=3600sec Now when actually converted 3600\1000 that would give u the two zero gets cut and remains is 36\10 that would give u after dividing each by 2 i.e 18\5which means (18m\5s)1.FRACTION Now the major calculation, Two object over here is Train and the Man consider them as A and B where A is the Train as we have to find the speed of the train then B is the speed of the Man is 5 so we get A-5 We had 125m the length of train time 10 seconds already these are in meters and in seconds no need to convert them so 125m\10s u get (25m\2sec) 2.FRACTION Now, finally get the first fraction and the second fraction together i.e (18\5)*(25\2)u get 45 as answer when u calculate then A-5=45 ,when u move the negative -5 to this side of the equals too sign it converts to positive giving u A=45+5 i.e 50 so A=50 and A is the speed of train!!hope u'll understood!!take care!!

 Monisha said: (Fri, Jul 15, 2011 05:13:47 AM) Great job guys!!! I understood well than my faculty teaches...

 Raja said: (Tue, Aug 2, 2011 11:30:36 PM) Thank you friends I understood well never before. Every one has given their own ideology with respect to problem.

 Umesh said: (Tue, Aug 9, 2011 02:33:06 PM) A train 125 m long passes a man, running at 5 km/hr in the same direction in which the train is going, in 10 seconds. The speed of the train is: ====> dist. travelled by man in 10 sec. = (5*5/18) *10=250/18 A train will have to travel its own length + dist.travelled by man. (when train will pass the man he would have travelled 125/9 m in same dir.) i.e. 125+125/9 meters = 1250/9 speed of train = (1250/9)/10 = 125/9 m/s=125/9 *18/5 = 50 km/hr

 Tarun Dumra said: (Fri, Aug 26, 2011 03:31:52 PM) Nice expalnation by ankita.

 Vandna said: (Sun, Sep 4, 2011 10:55:39 AM) Can anyone solve this? A train moving at 36Kmph takes 12 seconds to cross a platform. It takes 6 seconds to cross a man running at the rate of 9Kmph in the opposite direction. Find the length of the train.

 Shiwam said: (Fri, Sep 9, 2011 10:45:18 AM) @vandna It is option checking question so option must be given. Since it has 3 variables plateform length,train length & train speed. it might be done by option checking.

 Vijaya said: (Fri, Sep 9, 2011 03:52:38 PM) Hi amit and Sarah Here x - 5 = 45 x= 45 + 5 (when minus (-) simble comes from right of = to left of = it will become +.

 G.Humayun said: (Fri, Sep 23, 2011 09:43:11 AM) Thanks friends its very useful.

 Preetha said: (Fri, Sep 23, 2011 08:36:55 PM) Hi friends, I can't understand this please anyone help me in some other method.

 Gnana said: (Fri, Sep 30, 2011 01:42:48 PM) Very nice vandha.

 Sagar said: (Tue, Oct 4, 2011 11:52:18 PM) Finally we need to find speed me train. But in problem train speed is compared with moving object i.e man. So (total speed of train-speed of man=relative speed).

 Pradeep said: (Mon, Nov 7, 2011 12:09:51 AM) Can you please explain me what is relative speed here and why it is used here ?

 Nagaraj said: (Sun, Nov 20, 2011 02:23:23 AM) It should be taken as 1000/60*60 beacuse distance covered/ time taken.

 M.Kanna said: (Wed, Nov 23, 2011 08:23:23 PM) 18/5 explanation is super k/m h/r put 1000/3600=5/18 answer is very nice apserve then nice.

 Mahendra said: (Sat, Nov 26, 2011 11:33:46 PM) Nice explanation sheela thank you all who commented.

 Pradeep said: (Fri, Dec 9, 2011 06:30:43 PM) From The Question 5Km/hr So please explain it 1000/3600. give me reason.

 Kirubha said: (Wed, Dec 21, 2011 10:53:08 AM) FRNDS is it correct or not tell me plz.... MAN'S SPEED = 5 KM/HR Train length =125 m. let assume train speed=x. then we get relative speed (rs) of train and man is become rs=x-5. To conver km/hr into m/s. = (x-5) / (5/18) = 5x-25 / 18 speed = distance/time 125/10 = 5x-25 / 18 2250 = 50x-250 x = 2000 / 50 x = 40 Is it correct?

 Swapnil....... said: (Sat, Dec 24, 2011 07:10:25 PM) Why is it addition of 45km/hr & 5km/hr? Because I thing train & man is going to same direction that time sutract but in this case addition of 45km/Hr & 5km/hr please explain it why is it addition.

 Challu said: (Thu, Dec 29, 2011 07:18:23 PM) Think you are in a train, another one moving side by you in parallel, what will you experience? the train is in less speed of actualone. To find original speed you have to add your train speed.

 Preethi said: (Wed, Jan 4, 2012 11:51:15 AM) You are right kirubha. Nice explanation challu.

 Preethi said: (Wed, Jan 4, 2012 12:21:56 PM) Thanks Abhishek now I clear about relative speed.

 Hari said: (Fri, Jan 6, 2012 06:03:37 PM) Excuse me? Why we divided 125 with 10?. Please explain me.

 Ahmed said: (Sat, Jan 7, 2012 11:03:32 PM) Explanation given by ramesh chandra is very good and short, Please follow his process without wasting your time. We need such a good explanation like that.

 Uma said: (Fri, Jan 13, 2012 07:15:56 PM) Manoj explanation s superb. Thank you.

 Vinod Salunke said: (Wed, Jan 18, 2012 06:59:30 PM) Nice explanation by ramesh chandra.

 Akhil said: (Thu, Jan 19, 2012 03:30:30 AM) 18/5 = 1 km/hr = 1000/3600 m/s = 10/36 m/s = 5/18 m/s.

 Nirmal said: (Sun, Jan 22, 2012 08:45:22 PM) Vijay Kumar Kuppani you did solve problem very nicely again thanks.

 Shobi said: (Sat, Feb 11, 2012 06:35:26 PM) Hi friends, I ave confuesion in relative speed. Can I have some more explanation about relative speed?

 Shro said: (Wed, Feb 15, 2012 04:21:43 PM) Thanku Rahul. Your explanation was easy to understand and cleared my doubts too :).

 Jrr said: (Fri, Feb 17, 2012 10:47:21 AM) Abhishek's answer explaines this clearly...Thanks Abhishek!!!

 Ranjit R Pawar said: (Mon, Feb 27, 2012 05:18:03 PM) Thanks rahul.

 Anish said: (Tue, Mar 27, 2012 01:40:21 AM) Hi Manishkumar,Vijaykumarkuppani,Umesh U hav cleard the points exactly how itz done. Thanks a lot...

 Parvez Khan said: (Wed, Apr 4, 2012 01:30:53 PM) How was the relative speed calculated ?

 Ambikun said: (Wed, Apr 4, 2012 10:08:00 PM) There is no need of calculating relative speed. It can be solved easily by calculating the distance traveled by the man in 10 sec and the total distance covered by the train in the same time. This is very simple.

 Sanghaniakshay said: (Thu, Apr 12, 2012 11:52:28 PM) Thanks abhishek.

 Greeshma Reddy said: (Wed, Apr 18, 2012 10:15:17 AM) How did this equation x-5=45 form?

 Pradyumna Kumar Das said: (Fri, May 11, 2012 09:40:16 AM) If the man and train in opposite direction then it relative speed is x+5. And speed is x+5=45. =>x=40. Am I right?

 Sada said: (Thu, May 24, 2012 11:13:11 AM) Any basic formula is there for this problem kindly explain.

 Bhavesh Sharma/ Gadgad786 said: (Sun, May 27, 2012 07:01:56 PM) Why we are multiplying the 18/5 ? or we can ask that why we are divide ? The answer is simple. We are converting the 'kilo-meters/hour' value into 'meters/second'. Let me explain about converting km/hr into m/s in detail. 1 km = 1000 meters. 1 hr = 3600 seconds. 1 km/hr = 1000/3600 m/s = 10/36 m/s = 5/18 m/s. Therefore 1 km/hr = 5/18 m/sec. Similarly 60 km/hr = 60 x 5/18 m/sec. You may ask me, why should I convert it from km/hr to m/sec?

 Nil said: (Sun, Jun 3, 2012 03:13:31 PM) If we convert km/hr into m/sec i.e. 1000/3600 it's come 5/18. So why it is calculation is 125/10*18/5 instead of 5/18?

 Ravi said: (Thu, Jun 7, 2012 11:50:45 PM) It is given that Speed of man=5km/hr Distance travelled by man in 10s=125/9m Distance travelled by train in 10s= {125+(125/9)}m Hence Speed of train = [{125+(125/9)/10]*3600 = 50 km/hr

 Shailesh said: (Sat, Jul 7, 2012 09:41:41 PM) Speed of train=(length of train/time) is a formula hence, 125/10 m/sec now (125/10)*(18/5)=45.. multiply by 18/5 to become km/h now 45 is relative speed sr=s1-s2 45=s1-5 s1=50

 Chandu said: (Fri, Jul 20, 2012 09:00:18 PM) Why it is subtracted ? please explain.

 Vikram said: (Thu, Jul 26, 2012 02:48:05 PM) A Train 125m long passes a man,running at 5km/hr. It means that train speed =5000m/3600sec.------(1hr=60*60=3600sec & 1km=1000meters). & Second Train running on same Direction & Passed in 10sec's. It means Second train cross distance within 10sec's. Speed of Train for meters/10sec = 5000m/3600sec*10sec=1.388888888889m So,that train speed for km/hr=speed of train for 10 sec * remaining 3590 Seconds(3600-10). =1.3888888889*3590=49.8611111111111111=50km/hr. Therefore, A speed of that train=50km/hr.

 Bulldozzer said: (Sun, Jul 29, 2012 04:33:50 PM) This is simple. Length of the train is given and the seconds is given. So we have m/sec there. To convert it to km/hr, 1km= 1000 m and 1 hr = 3600 sec. So km/hr= 1000/3600. So we have 18/5. Now we got our km/hr. Well that guy is running at 5 km speed. So we take the train speed as x and subtracting the 5 km speed from that. We have x-5 as the train speed. Now x-5= 45. So x= 45+5=50. :-).

 Kishore Kumar said: (Fri, Aug 3, 2012 01:11:47 PM) Your running at a speed of 5km/hr (1km=1000 meter and 1hr=3600seconds,which will be 1000/3600=10/36=5/18) Note :for 1 km/hr Therefore 5(given km)*5/18=1.39 ------------------------------- Meanwhile 125m long train crosses you in 10 seconds along with you in same diretion. Then!! 125/10 i.e its in the form of (125)m/(10)s. ------------------------------- So add those two values in the form of m/s,which is 13.89=a ------------------------------- Now question to find speed of the train,since we found in the form of m/s,but the options provided are in the form of KM/HR ------------------------------- So to convert M/S to KM/HR : (a*18/5)=(13.89*3.6) Gives answer as 50 km/hr

 Sunil said: (Sat, Aug 18, 2012 10:37:30 AM) How/ why Let the speed of the train be x km/hr. Then, relative speed = (x - 5) km/hr. Please any one explain me why let speed =(x-5)km hr.

 Harish said: (Fri, Aug 24, 2012 11:45:13 AM) It is brain storming and conceptual question .Thank you for giving more explanation on this question.Thank you very much....!

 Karthik said: (Fri, Aug 24, 2012 08:36:54 PM) 125/10 = 25/2 25/2*18/5 = 450/10 45 friends, i don't know how to solve this problems after this so plz anyone help me out

 Anbu said: (Tue, Sep 4, 2012 01:59:17 PM) Just try this 1 sec 5 km/hr means 10 sec is 50 km/hr thats it.. becoz the man running at same time train is moving ..

 Preethi said: (Sun, Sep 16, 2012 07:07:21 PM) Abisheks answer is realy nice. Thank you abi.

 Mamatha said: (Tue, Sep 18, 2012 03:33:19 PM) To convert km/h into m/s we multiply that value with 5/18.why is this because 1km=1000m 1h=60min*60sec=3600sec now 1km/h=1000/3600=5/18 if we want to convert m/s into km/h we have to multiply with 18/5. hope you can understand.

 Susmitha said: (Tue, Sep 18, 2012 08:20:32 PM) x-5 is nothing but here x refers to the speed of train and as both train and boy are moving in the same direction relative velocity comes into picture and here relative velocity is the difference of two velocities.

 Mani Sharma said: (Thu, Sep 20, 2012 01:26:35 PM) If train moving same direction = SUBTRACTION OCCUR. If train moving opposite direction = ADDITION OCCUR.

 Sundeep said: (Thu, Sep 27, 2012 10:35:56 PM) Let the speed of the train is x km/hr Then the relative speed is (x-5)km/hr Therefore, Time = 10sec Distance = 125m Speed = (x-5)km/hr As we are calculating in m/sec so we have to convert km/hr to m/sec. (x-5)*1000/3600 m/sec or (x-5)*5/18 {by cancelling by 200. 200*5=1000,200*18=3600} Therefore , Speed = distance/ time (x-5)5/18 = 125/10 x-5 = 125*18/10*5 x-5 = 2250/50 x-5 = 45 x = 45+5 x = 50 Therefore x is 50km/hr (speed of the train)

 Vinothini said: (Thu, Oct 4, 2012 10:11:45 PM) Hai friends I want to give small tips. If there train passes in same direction just subtract it. If train passes in different or opposite direction direction just add it. If you need to convert km/pr use this formula (a*5%18) for speed and m/sec the formula is (a*18%5).

 Bibin said: (Sun, Oct 28, 2012 12:18:37 PM) Why you made it 18/5, earlier it was 5/18, please explain me.

 Jayan said: (Tue, Nov 20, 2012 09:05:35 AM) Here x=45 is speed of per 1km. question is 5km/hr . So x-5=45 x=45+5 x=50 Thats all.

 Anvesh said: (Thu, Nov 29, 2012 03:04:37 PM) l=125m; s=5*5/18; t=10s; l=t*s; s=t/l; s=125/10; s=12.5*18/5; the man was also going same direction so, s=45+5; s=50;

 Charles @ Redhills said: (Wed, Dec 5, 2012 01:53:34 PM) Let the speed of the train is 'x' Length=125m Speed=10s --> as per "Length of the train = speed X time" --> 125m = 10s.x --> x=(125m/10s) X (360/360)=(360 X 125m)/3600s --> =45000m/3600s = 45km/1hr As the above value is relative with the speed of man whose speed of running is 5km/1hr also to be added for the exact speed of the train. There fore.. -->exact speed of the train is = (45km/1hr)+(5km/1hr)=50km/1hr I believe its simple and right answer.

 Jagadeesh said: (Mon, Dec 31, 2012 12:31:57 PM) Let relative velocity of train with respect to man be vtm,actual velocity of train Be vt and velocity of man be vm. We know that vtm=vt-vm, But from problem vtm is =length of train/time taken =(125*18/5)/10 =45 km/hr. From above actual speed of train is,vt=vtm+vm =45+5=50 km/hr.

 Preethi said: (Wed, Jan 30, 2013 11:07:08 AM) A train of length 110mtr travelling at a speed of 80km/hr. Find the time taken by that train to overtake a train having length 130mtr travelling at a speed of 62km/hr?

 Malik said: (Mon, Feb 25, 2013 12:39:12 PM) @Preethi. Relative speed u-v = 80-62= 18km/hr=(18* 5/18)= 5 m/s. Total length a+b = 110+130= 240 m. Time to overtake = (a+b)/(u-v)[see formula 9 from formula section] = 240/5 = 48 sec. Am I correct?