Question

A ball of $50g$ strikes a smooth wall with speed $20m/s$ as shown. If collision is elastic and contact period is $2\times {10}^{-3}s$, the force exerted by the wall on the ball is

• A. $500N$ to right
• B. $250N$ to right
• C. $250N$ to left
• D. $500N$ to left

Answer 1

The correct option is A $500N$ to right

Step 1: Draw a labelled diagram.

Step 2: Find the force exerted by the wall on the ball.

Mass of the ball $m=50g$
Speed of ball $=20m/sec$
Time of collision $=2\times {10}^{-3}s$

Change in momentum in $y$− direction.
$\Delta p_y=0$

Change in momentum in $x$− direction.

$\Delta p_x=mv\cos {60}^{\circ }-(-mv\cos {60}^{\circ })$

$2mv\cos {60}^{\circ }=mv$

$F_x=\frac{\Delta p_x}{\Delta t}=\frac{mv}{\Delta t}=\frac{50\times {10}^{-3}\times 20}{2\times {10}^{-3}}$

$=500N$, to the right