### Discussion :: Kinematics of Particle (KOP) - General Questions (Q.No.1)

Veni said: (Dec 21, 2010) | |

How answer will come? Please explain. |

Abhishek Chouksey said: (Apr 15, 2011) | |

Its Simple> in first 10 sec it reaches only 40 m/s=1/2*10*8(uniform acc) in next 1.25 sec at constant acc.(v=u+at) it tends to 50 m/s. |

Puru said: (Jun 3, 2011) | |

Dear, please tell me how it comes 40m/s. By which law and logic you calculate 40m/s. FYI 1. V=u+at 3. v2=u2+2as 2. s=ut+1/2at2 4. s=1/2(v+u)t |

Gopala Krishna said: (Jun 30, 2011) | |

Here the car is not moving with uniform accleration upto ten seconds area of the triangle=0.5*8*10=40m/sec(t=10) now accleration is constant So apply v=u+at 50=40+8*t t=1.25 So total timet = 10+1.25 = 11.25 |

Mani said: (Aug 25, 2011) | |

S=1/2 (8+0) 10. Since initial velocity is zero. My guess. |

Santhosha said: (Aug 31, 2011) | |

Initially the is at rest, we consider u=40m/s, and v=50m/s then v=u+at 50=40+8*t t=1.25sec, This is the time required to travel from 40m/s velocity to 50m/s velocity. then the time required to travel the car from rest position is 10+1.25=11.25 sec. |

Ankit Bhardwaj said: (Sep 24, 2011) | |

That's very simple... We know dat a= dv/dt or we can say that v= integral(a dt)...............(1) Now by graph we can see that a=(4/5)t upto the first 10 seconds Now put v=50 in the eq.(1) So after calculating t= 11.25 sec. |

Sekhar said: (Sep 15, 2012) | |

Actually we want calculate and differentiating function, like ankith what he was explain. |

Wasprulez1990 said: (Oct 7, 2012) | |

The area in the graph is velocity i.e. v=at, so the total area is given i.e.final velocity 50 m/s, So 50= area of triangle + area of rectangle. 50= (0.5 x base x height) + (width x height). 50= (0.5 x 10 x 8) + [ (t-10) x 8]. Finally t=11.25 seconds. |

Aishwarya Katale said: (Dec 2, 2013) | |

How to calculate 40? which is v? |

Ankit Kumar said: (Oct 27, 2014) | |

Aishwarya Katale : Actually 40m/s its area under the curve. :-). |

Manan said: (Dec 7, 2014) | |

The answer is incorrect correct answer is 6.25s. Solution u = 0. v = 50 m/s. a = 8 m/s^2. So just find t by v = u+at. Which is 50 = 0+8t? 50 = 8t. t = 50\8 = 6.25s. |

Hasya said: (May 17, 2016) | |

No, 11.25 is correct. The formula v = u + at is applicable only in the case of constant acceleration. Since up to the first 10 seconds the car is moving wth increasing acceleration area under the triangle gives final velocity at t =10 sec since initial velocity is 0. |

Kumara Swamy said: (May 31, 2016) | |

11.25 secs are the correct answer. Equations of motion are: v = u + at;. s = ut + 0. 5 at^2 etc are valid when accleration is constant. In the question, the acceleration varies with timeup to 10 sec and then it is constant so, use v = u + at after 10 secs. And for before 10 secs use an area under a - t graph is the velocity similarly area under v - t graph gives displacement. You will understand this concept when you pass through basics of calculus. |

Srikanth said: (Aug 10, 2016) | |

Acceleration * time = velocity. So,in the above graph find the area covered by line up to uniform acceleration. i.e., Area of triangle = 1/2 * 10 * 8 = 40 m/s. And then it follows constant acceleration and the required area(rectangle) is 10. So 8 * 1.25 = 10 m/s, so a total of (40 + 10)m/s is achieved in (10 + 1.25)secs. |

Ss Ahamed Halith said: (Oct 10, 2019) | |

1. We consider the given acceleration and time (i.e a=8 ms-2 t=10s) then we find velocity for that next we pick any one choices given and add or sub for making it equal to 10 find another velocity. |

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