A 0.5 kg ball moving with a speed of 12 m/s strikes a hard wall at an angle of 30° with the wall. It is reflected with the same speed at the same angle. If the ball is in contact with the wall for 0.25 seconds, the average force acting on the wall is

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(3) 24 N. Given: m=0.5 kg, v=12 m/s, 30° measured from the wall, Δ t=0.25 s. Idea: only the component perpendicular to the wall reverses; the component along the wall is untouched. Since the angle is measured from the wall, the perpendicular component is v sin 30°=12×1/2=6 m/s. Change in momentum: Δ p=2mv sin 30°=2×0.5×6=6 kg m s⁻¹. F=(Δ p)/(Δ t)=6/(0.25). F=24 N. By Newton's third law the wall feels the same 24 N.

A 0.5 kg ball moving with a speed of 12 m/s strikes a hard wall at an angle of 30° with the wall. It is reflected with the same speed at the same angle. If the ball is in contact with the wall for 0.25 seconds, the average force acting on the wall is

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