Question

A empty rail car of mass 100 kg is at rest on the railway track. a boy of mass 40 kg running with a speed of 5 meter per second jumps on the rail car. the speed of the (car + boy) system is how much?

Answer 1

Kinetic energy =  $\frac{1}{2} m v^{2}$


Kinetic energy before he jumped = Kinetic energy after he jumped


1/2 x 40 x 5² = 1/2(100+40)v²

1000 = 140v²


      v² = 1000/140 = 50/7

      v = 2.67 m/s


The boy and the car are moving at a velocity = 2.67m/s

Answer 2

Answer:is 1.43

Explanation:

We know mass of rail = 100kg

Mass of boy = 40 kg

Initial speed of rail = 0

Initial speed of boy = 5m/s

We have to find final velocity

M1v1 + m2v2= m1v1+ m2v2

0+200= 100v + 40v

200 ÷ 140 = 1.42 m/s