A 0.5 kg ball is thrown horizontally towards a wall with a speed of 10 m/s. The

Question

A 0.5 kg ball is thrown horizontally towards a wall with a speed of 10 m/s. The initial velocity is chosen to be the positive x -direction for this question. The ball horizontally rebounds back from the wall with a speed of 10 m/s in the negative x -direction. What is momentum of the ball before it hits the wall, p? What is momentum of the ball after it hits the wall, p,? What is the change in momentum of the ball, delta p? (Give both magnitude and direction for each answer.) Is momentum conserved for the ball?

Explanation / Answer

m=0.5 kg

u = +10 i m/s

v = -10 i m/s

pi = mu = 0.5 * 10 = 5i kg m/s : magnitude :5, direction: +x

pf = mv =0.5 * -10 = -5i kg m/s : magnitude:5, direction: -x

change in momentum: delta p = pi - pf = 5i - (-5i) = +10i kg m/s : magnitude: 10, direction : x

Momentum is not conserved for the ball as change in momentum is not zero. However momentum will be conserved for the 'ball+wall' system.

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