Civil Engineering - Hydraulics - Discussion

5. 

If the atmospheric pressure on the surface of an oil tank (sp. gr. 0.8) is 0.1 kg/cm2, the pressure at a depth of 2.5 m, is

[A]. 1 metre of water
[B]. 2 metres of water
[C]. 3 metres of water
[D]. 3.5 metres of water
[E]. 4.0 metres of water.

Answer: Option C

Explanation:

No answer description available for this question.

Kanishk said: (Sep 10, 2013)  
How come the answer is C?

Initial Pressure in terms of ht. of water column= 1000/(1000*10)=0.1 m --- (i).

Pressure @ 2.5 m depth in oil tank = 2.5*800*10.

Representing above pressure as ht of water column, the answer comes out to be 2.0 m --- (ii).

(i) + (ii) = 2.1m.

Nikku said: (Oct 5, 2013)  
Pressure head in terms of water = 2.5/0.8 = 3.1m.

Hitesh Kumar said: (Dec 12, 2013)  
Total pressure = ((.1*10^4)/1000)+(.8*2.5) = 3.

Kumar said: (Nov 27, 2014)  
Initial pressure is 1000 kg/m^2.

Pressure at 2.5 m depth is 19620 kg/m^2.

Total pressure at a depth 2.5 m is = 19620+1000 = 20620 kg/m^2.

Depth in terms of water = 20620/(1000*9.81) = 2.1 m.

Ruben said: (Mar 3, 2015)  
From Basic Hydro static principle (FM text book by Frank m White).

P = Pa-Gamma (Z2-Z1).

Where Pa = Atmospheric pressure in n/m2 Z1 = 0 (Reference surface) and Z2 = negative downwards.

= (0.98 n/m2-7848(-2.5)).

= 19620.8 pa.

H = (19620.8/(1000*9.81)) = 2 m of water.

Nikita Patil said: (Mar 12, 2015)  
How do you calculate the pressure at the given height? Please explain me.

Manpraveen said: (Mar 25, 2015)  
P = $gh.

Pressure for oil = 0.8*1000*9.81*2.5 = 19620 n/m^2.

Pressure for water = 1000*9.81*h = 19620.

H1 = 19620/9810 = 2 m.

H2 = atmospheric head = p/$g.

H2 = 1000*9.81/1000*9.81= 1 m.

Total head = H1+H2 = 2+1 = 3 m (Answer).

Ma Murtaza said: (Jun 17, 2015)  
p*ATM = 0.1 kg/cm*2 = 1000 kg/m*2 = 9810 N/m*2.

p*oil = 19620 N/m*2 (after calculation).

Total pressure = 29430 N/m*2.

Hence, h*water = 29430/9810 = 3 m of water.

Abdilahi Khalif said: (Jun 18, 2015)  
1000/(1000+2.5*0.8) = 3.

Rizgar Karim said: (Jul 27, 2015)  
Patm = 0.1kg/cm2 = 0.1*10000*9.81/1000 = 9.81 KN/m2.

Poil = 0.8*9.81*2.5 = 19.62 KN/m2.

Ptotal = Patm + Poil.

Ptotal = 19.62 + 9.81 = 29.43 KN/m2.

P in-term of water = 29.43/9.81 = 3m of water.

Ccjayesh said: (Feb 9, 2016)  
Pa = 0.1 kg/cm2 = 1000 kg/m2.

Poil = 800*2.5 = 2000 kg/m2.

Total = 3000 kg/m2 = 3000/1000 = 3 meters of water.

Anonymous said: (Jul 30, 2016)  
P2 = P1 + Density(H); P1 = 0.1kg/cm^2 or 1000kg/m2.

Density of oil = specific Gravity x 1000 kg/m3.
= 800kg/m3 (Note: 1000kg/m3 is the density of water).
P2 = 1000 + 800 x 2.5 = 3000kg/m2.
Pressure in H of Water = 3000/1000 = 3.0m.

Kailash Paliwal said: (Sep 18, 2016)  
Atmosphere pressure =.1kg/cm2 = 1000 kg/m2.

1000kg/1000kg = 1m of water.

Oil pressure = 2.5m = 2.5 *.8 = 2m of water. Total height = 1 + 2 = 3 m. Hence c is right.

Bahram said: (Oct 4, 2016)  
First Patm = 0.1kg/sq/cm = 1000 kg/sq.m.
Now Poil = S(oil) * ρ(water) *h(oil) => 0.8 * 1000 * 2.5 = 2,000 kg/sq.m.

So, P(total at bottom) = 2,000 + 1,000 = 3,000 kg/sq.m.

Now h(pressure in terms of head of water) = P(total)/ρ(water) => 3,000 kg/sq.m/1,000 kg/cu.m = 3 m of water.

Komala Sai said: (Dec 22, 2016)  
Patm = 0.1kg/cm^2
=> 1000kg/m^2.

Poil = (0.8 * 1000) * 2.5
= 2000 kg/m^2.

Finally in terms of water = (1000 + 2000) ÷ 1000,
= 3m of water.

Rajani Patel said: (Feb 7, 2017)  
Pressure at surface =10000kg/m^2.
Pressure at a depth of 2.5 m=(2.5*9.81*800)=19620.
Total pressure=29620.
H=P/1000*9.81=29620/1000*9.81.
H = 3.01m of water.

Anonymous said: (Feb 20, 2017)  
I think the answer should be 2 m. Because the atm pressure will be same for both oil surface and water surface. So it will be neglected.

Please reply if anyone thinks I'm wrong. And do explain. Thanks.

Jeevan said: (Feb 23, 2017)  
Specific Gravity of oil is .8 & water is 1. So oil has less density the water therefor, water shows less head. So, the answer will be 2m not 3.

Sashaus said: (Apr 6, 2017)  
S1 h1 = s2 h2 or £1h1 = £2h2.
£ = density , s= sp.gr.

1000 h1 = 800 * 2.5.
H1 = 2 + 1 (initially pressure is 1) = 3.

Er. Dipesh Yadav said: (Apr 15, 2017)  
Atmospheric pressure = 0.1 * 9.81 * 100 * 100 = 9810 N/m2.
Pressure at 2.5m depth = 0.8 * 9810 * 2.5 = 19620 N/m2.
Total pressure at depth 2.5m = 9810 + 19620 = 29430 N/m2.
Height in terms of water= 29430/9810 = 3m.

Makar said: (Apr 28, 2017)  
Yes, correct @Dipesh.

Makar said: (Apr 28, 2017)  
1 kg/m2 = 1000kg/cm2 this are correct.

Suresh Yadav said: (May 26, 2017)  
Yes, your answer is correct. Thank you @Dipesh.

Gurmeet said: (Sep 25, 2017)  
Simply P = density * gh.

Waqar Ahmed Awan said: (Dec 28, 2017)  
We know that;

1kg=9.81N and 1m=100cm.
let atmosppheric pressure at top surface be; P1=denssity*g*h=0.1kg/cm2=0.1*9.81*100*100=9810N/m2.
let pressure at heigt of 2.5m be p2=0.8*1000*9.81*2.5=19620N/M2.
now total pressureP =p1+p2=9810+19620=29430N/m2.
NOW pressure in terms of water =P/p1=29430/9810=3m so option C is correct.

Prashant said: (Mar 24, 2018)  
How (total pressure/atm pressure) is equal to the pressure head of water?

Please explain anyone.

Thanks.

Nani Abdul said: (Aug 1, 2018)  
Patm + (0.8)(2.5m)(9810N/m3) = Hh2o(9810N/m3).

Patm = 0.1Kg/cm2 --> 1000Kg/m2.
Patm = 1000Kg/m2(9.81m/s2) --> 9810N/m2 (Pa).

9810N/m2 + (0.8)(2.5m)(9810N/m3) = Hh2o(9810N/m3).
Hh20 = (9810N/m2 + (0.8)(2.5m)(9810N/m3))/9810N/m3.
Hh20 = 3mts.

Amare Yihunie said: (Feb 2, 2019)  
Specific gravity oil = 0.8.

Density of oil=0.8*1000=800 kg/m3
Atmospheric pressure at surface of oil=0.1 kg/cm2=0.1*10000*10=20,000 pascal
Pressure of oil at depth of 2.5 m = 800 * 2.5 * 10 = 10,000 pascal.

Total pressure = 10,000 + 20,000 = 30000 pascal.

In terms of water depth pressure = density of water * depth of water * gravity.

The Depth of water = pressure/density * gravity = 30,000/(10000*10) = 3 meter.

Govind said: (Feb 17, 2020)  
The pressure at the bottom is 2.5x0.8x9.81= 19.62 KN/M3.
Initial pressure at top= 0.1 kg/cm2= 0.1x98.06=9.80 KN/M3.
Total pressure at Bottom =19.62+9.80 =29.42 KN/M3.
Head= 29.4/9.81 =2.99 =3.00 Metre.

Saurabh Kaday said: (Mar 5, 2020)  
Don't understand clearly.

Anyone, please solve it by standard formula with step by step with meaning.

Ravinder said: (Apr 11, 2020)  
Patm=0.1kg/cm^2=10,000Kg/m^2.
Pressure at 2.5m=0.8*1000*0.8*2.5=19620Kg/m^2.
Total pressure at 2.5m=10,000+19620=29620Kg/m^2.
But in option, we need pressure in terms of head=Pressure/(Density*g)
H=29620/(9.81*1000)=3.1~3m of water column.

Pawan Pandey said: (Apr 22, 2020)  
0.1*10^4 kg/m2= 1000 kg/m2.
0.8*1000*2.5= 2000 kg/m2,
1000+2000= 3000 kg/m2 ( pressure ),
3000/1000= 3 m of water.

Pavan said: (May 3, 2020)  
How the pressure at 250 cm comes out as 2000 Kg/m2?

That will be $gh, we don't consider 'g' value.

Can anyone explain me?

Vikas said: (Nov 11, 2020)  
If we will consider the value of g then the pressure will come in the unit of Newton/square meter.

For determining the value of pressure in the form of kg/m2 we can't use Value of g.

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