Question

A $3\,kg$ ball strikes a heavy rigid wall with a speed of $10\,m /s$ at an angle of $60\,^\circ$ with the wall. It gets reflected with the same speed (in the same plane) at an angle of $60\,^\circ$ with wall. If the ball is in contact with the wall for $0.2\, s$, the average force exerted on the ball by wall is

• A. 150 N
• B. zero N
• C. $150\sqrt3\, N$
• D. 300 N

Answer 1

Answer: (C)

$150\sqrt3\, N$

Answer 2

$F \times t = \Delta p = 2 \, m \upsilon \, \cos \, \theta$ ($\therefore$ sin components concel out ) $\therefore\:\:\: F = \frac{2 m \upsilon \, cos \, \theta }{t} = \frac{2 \times 3 \times 10 \, cos \,60^\circ}{0.2} = \frac{6 \times 10 \times 0.5}{0.2}$ = 150 $\sqrt {3}$ N