A 10 gram ball is thrown horizontally at a wall with speed 15 m/s and bounces back with the same speed. The magnitude of the impulse on the ball is? The answer is 0.3 N s but how do you come up with that answer?
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Impulse is the change in momentum of the object. Its initial momentum is p=mv which is p=(.01kg)(15m/s)=0.15kg*m/s. Its final momentum is the same magnitude but opposite in direction since the velocity faces the opposite direction. Thus p=(.01kg)(-15m/s)=-0.15kg*m/s. Impulse would be momentum final minus momentum intial or (-0.15kg*m/s)-(0.15kg*m/s)=-0.30kg*m/s. Taking the right to be positive and the left to be negative in direction would give you positive 0.30 as your answer, it all depends on your reference frame.