Question

A ball of mass $ 0.1\,kg $ strikes a wall normally with a speed of $ 30\,ms^{-1} $ and rebounds with a speed of $ 20\,ms^{-1} $ . The impulse of the force exerted by the wall on the ball is

• A. $ 1\,N $ - $ s $
• B. $ 5\,N $ - $ s $
• C. $ 2\,N $ - $ s $
• D. $ 3\,N $ - $ s $

Answer 1

Answer: (B)

Impulse = Change is momentum $p_{i}-p_{f}$
direction of $p_{f}$ and $p_{i}$ apposite to each other
$\therefore $ Impulse $=mu-(-m v)$
$=mu+m v=m(u+v)=0.1(30+20) $
$=0.1 \times 50=5 N - s$