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A hockey player hits a ball with an impulse of 15 Ns. If time of hit is 0.2 s, the average force exerted by the player on the ball is

  • A.75 N
  • B.50 N
  • C.15 N
  • D.20 N
  • E.25 N

Answer: A

The average force is 75 N.

Impulse is average force times the time of contact, \(J = F\Delta t\):

\[ F = \frac{J}{\Delta t} = \frac{15}{0.2} = 75\ \text{N} \]

15 N treats the impulse as the force, and 50 N or 25 N come from slips in dividing by 0.2.

Impulse equals the change in momentum, so the ball's momentum changes by 15 kg m s-1 whatever its mass; a shorter contact time would mean a larger force for the same impulse.

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