Medium
A cricket ball of mass 0.15 kg moving at 20 m/s is stopped by a fielder in 0.1 s. What is the average force exerted by the fielder on the ball?
Explanation
Explanation
Step 1: Initial momentum = mass × velocity = 0.15 × 20 = 3 kg m/s.
Step 2: Final momentum = 0 because the ball stops.
Step 3: Change in momentum = 0 − 3 = −3 kg m/s (magnitude 3 kg m/s).
Step 4: By Newton's second law, F = change in momentum ÷ time = 3 ÷ 0.1 = 30 N.
Step 5: The negative sign only shows that the force acts opposite to the ball's motion.
Answer: 30 N.
PRO TIP
Re-check your working by substituting the answer back into the original question.