Physics problem help

Question

A 0.060 kg tennis ball, initially moving at a speed of 12 m/s, is struck by a racket causing it to rebound in the opposite direction at a speed of 18 m/s. What is magnitude of the force exerted on the ball by the racket assuming a collision time of 0.15 s?

Select one:

a. 2.4 N

b. 4.8 N

c. 7.3 N

d. 12 N

Answer 1

Calculate the change in linear momentum of the ball, set it equal to the impulse, and then solve for the force.

m = mass of ball = 0.060 kg

v₁ = initial velocity of ball = +12 m/s

v₂ = final velocity of ball = -18 m/s

Δt = duration of collision = 0.15 s

F = applied force = ?

m(v₂ - v₁) = FΔt

F = m(v₂ - v₁) / Δt

Now plug in the numbers and get F in newtons. Be careful with signs! You should get -12 N (i.e. magnitude is 12 N). The minus sign means the force was applied in the direction opposite to the initial direction of motion of the ball.