Question

Assume that a 15-kg ball moving at 8 m/s strikes a wall perpendicularly and rebounds elastically at the same speed. What is the amount of impulse given to the wall? Be sure to show all work to support your answer.

Answer 1

So we are told that the ball rebounds elastically. What this means momentum and kinetic energy is conserved. So our initial condition equals our final condition.

Our initial condition is when the ball is moving at 8m/s and is 15 kg.

$p_0 = (8m/s)(15kg) = 120kg*m/s$

Next we our told it bounces off in the negative direction moving at 8m/s

$p_f = (-8m/s)(15kg) = -120kg*m/s$

Impulse, denoted as J, which is the change in momentum.

$J=p_f-p_0 = -120kg*m/s - 120kg*m/s = -240kg*m/s J = -240kg*m/s$

Hope this helps! :D