A boy is running with a velocity of 2 ms−1. He jumps over a stationary cart of 2 kg while running. If the mass of the boy is of 20 kg, find the velocity at which the cart moves after he jumps over the cart. (Neglect friction between the cart and ground)
Given mass of the boy, m1=20 kg
Initial velocity of boy, u1=2 ms−1
Given mass of the cart, m2=2kg
Initial velocity of the cart, u2=0 (Initially at rest)
Let v1 be the final velocity of the boy and v2 be the final velocity of the cart.
Since,the boy jumped over the cart, the final velocity v1 of boy will be equal to that of the cart.
Therefore v1=v2
According to law of conservation of momentum:
m1u1+m2u2=m1v1+m2v2
Sustituting the values , we get,
20×2+2×0=20×v1+2×v2
⇒40=20×v2+2×v2
⇒40=(20+2)×v2
⇒4022=v2
⇒v2=1.81 ms−1
Therefore, velocity of the cart after he jumps over it is equal to 1.81 ms−1.