Question 7
A ball of mass 0.1kg approaching a tennis player with a velocity of 10ms-1 is hit in the
opposite direction with a velocity of 15ms-1.If the time of impact between the racket and the
ball is 0.01 second, calculate the magnitude of the force with which the ball was hit.
Observation
The Chief Examiner reported that this question was well attempted by some candidates. However, majority of them did not take into
cognizance the opposite direction as indicated in the question.
First, the change in momentum is 𝑚(𝑣−𝑢)=(0.1)(15−(−10)) = (0.1)((25) = 2.5.
Therefore, Ft = 2.5 and the magnitude of force is 𝐹= 2.5⁄ 0.01 = 250 N.