Question

A tennis ball of mass 50g is hit against a wall. It hits the wall going right at 5 ms^-1 and rebounds to the left at 4 ms^-1, changing its momentum by 0.45 kg m/s left.

If the ball is in contact with the wall for 0.2 s what is the average force applied by the wall on the ball (your answer is a vector)?

Select one:

a. 2.25 N Left

b. 0.45 N Right

c. 0.45 N Left

d. 2.25 N Right

e. 0.09 N Left

Answer 1

tennis ball mass ,m = 50g

ball hits the wall going right at 5 ms-1 and the ball rebounds to the left direction at 4 ms-1.

ball is in contact with the wall for ,Δt =   0.2 s

change in momentum (ΔP) = 0.45 kg m/s left

Impulse is the change of momentum (ΔP) of an object when the object is acted upon by a force for an interval of time.  The formula for impulse or ΔP  = Force * Δt

0.45 = Force * ( 0.2)

2.25 N = Force.

as the net change in momemtum (ΔP) is in the left direction so the net applied force by wall is also  in left direction.

the average force applied by the wall on the ball is 2.25 N towards left.

So the option a is correct.