A ball with a mass of #6 kg# moving at #8 ms^-1# hits a still ball with a mass of #4 kg#. If the first ball stops moving, how fast is the second ball moving?

1 Answer
David G.
Jan 14, 2016

The total momentum before the collision is equal to the total momentum after. This means the second ball is moving at #12 ms^-1#.

Explanation:

The total momentum before the collision is in the moving ball: a stationary object has #0# momentum. The momentum for the moving ball is given by:

#p=mv = 6kg *8ms^-1 = 48 kgms^-1#

Momentum is conserved: the total momentum after the collision is the same as the total momentum before. The momentum is all on one ball since the other is now stationary.

#p =mv#

Rearranging: #m = p/v = 48/4 = 12 ms^-1#.

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