Question

A ball of mass $2kg$ is connected to a string of length $1m$ and made to move in a horizontal circle on a smooth frictionless table with a constant speed of $2m/s$. The other end of the string is connected to a fixed peg on the table. Find the magnitude of the average impulse exerted by the string on the ball in half a revolution.

• A. $0$
• B. $8Ns$
• C. $4Ns$
• D. $2\sqrt{2}Ns$

Answer 1

The correct option is B $8Ns$

Initial momentum, $P_i=mv\hat{j}$

After half revolution, final momentum, $P_f=-mv\hat{j}$

Impulse $J=P_f-P_i$

$J=-2mv\hat{j}$

Given: $m=2kg;v=2m/s$

Thus $|J|=2\times 2\times 2=8Ns$