A 5.00 kg dog runs towards a skateboard with a speed of 2.50 m/s. The skateboard is initially at rest. The dog jumps onto the skateboard and both the dog and skateboard move with a speed of 2.00 m/s. What is the mass of the skateboard? Assume that all motion is in the x direction.

The mass of the skateboard is 1.25 kg.

Explanation:

We have,

Mass of dog, m = 5 kg

Initial speed of dog, u = 2.5 m/s

Initial speed of skateboard, u' = 0 (at rest)

The dog jumps onto the skateboard and both the dog and skateboard move with a speed of 2.00 m/s. It is the common speed of the dog +skateboard, V = 2 m/s. We need to find the mass of the skateboard. Using conservation of momentum as :

m' is mass of skateboard

So, the mass of the skateboard is 1.25 kg.