# Momentum question

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a one-tonne spacecraft which is travelling at a speed of 9500 m/s is hit by a piece of debris of mass 0.5kg travelling at right angles to it at the same speed. As a result of the impact, the debris melts into the wall of the spacecraft leaving a 12cm hole.
Estimate the average force acting during the impact

Here is what I attempted to do:
F = m(v-u) / t

Momentum of spacecraft before: 1000*9500
Momentum of debris before: 0.5*9500

Velocity of spacecraft after: 9495 m/s (because 1000.5/(1000*9500))
Velocity of debris after: 13431.5 m/s

Momentum spaceship after: 1000*9495
Momentum debris after: 0.5*12431.5

Change in momentum of spaceship: mv-mu = 5000
Change in momentum of debris: -1965.75

Total change in momentum = 3034.25

Time: 0.12/9500

This gives me a force of 240 MN but the answer at the back of the book is 376 MN. Where have I gone wrong?
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