Question

A boy of mass 43.1 kg is initially on a skateboard of mass 2.00 kg, moving at a speed of 10.4 m/s. The boy falls off the skateboard, and his center of mass moves forward at a speed of 10.9 m/s. Find the final velocity of the skateboard.

Answer 1

In such problem, we can use the conservation of momentum.

By the conservation of momentum, Initial momentum = final momentum

Where , are the mass of boy and skateboard, is the initial velocity of the combined system and are the final velocities of boy and skateboard respectively.

Putting, ,, ,  

We get

Here negative sign indicates that the velocity of the skateboard is in backward direction just after falling down the boy.