Question

A boy throws a 4-kg pumpkin at 8m/s to a 40kg girl on roller skates, who catches it. At what speed does the girl then move backwards?

Answers

Assume the girl was facing the boy, and was stationary before catching the pumpkin.

Her initial momentum is zero.
Momentum of the punmkin
= 4 kg * 8 m/s
= 32 kg-m/s

Combined mass of girl and pumpkin
= 4+40
= 44 kg

Final velocity
= 32 kg-m-s<sup>-1</sup> / 44 kg
= 8/11 m/s

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