Question

Kevin has a mass of 87 kg and is skating with in-line skates. He sees his 22-kg younger brother up ahead standing on the sidewalk, with his back turned. Coming up from behind, he grabs his brother and rolls off at a speed of 2.4 m/s. Ignoring friction, find Kevin’s speed just before he grabbed his brother.

Answer 1

`V_ k = 3 m/s`

Step-by-step explanation:

Using the conservation of the linear momentum P:

`P_i = P_f`

so:

`M_kV_k = M_sV_s`

where
`M_k` is the mass of kevin,
`V_k` is the velocity of kevin before he grabs her brother,
`M_s` is the velocity of her brother and him after grabs her brother and
`V_s` is the velocity of both after the collition.

So, replacing the values and solving for Vk, we get:

`(87 kg)V_k = (87 kg+22 kg)(2.4m/s)`

`V_ k = 3 m/s`