Question

A hockey ball of mass $100g$ traveling at $10m{s}^{-1}$ is struck by a hockey stick so as to return it along its original path with a velocity at $5m{s}^{-1}$. Calculate the change of momentum occurred in the motion of the hockey ball by the force applied by the hockey stick:

• A. $1.5kgm/s$
• B. $5kgm/s$
• C. $1kgm/s$
• D. All

Answer 1

The correct option is A $1.5kgm/s$

Given, mass of ball $=100g=0.1kg$
initial velocity of ball $\left(u\right)=10m/s$
final velocity of ball $\left(v\right)=-5m/s$
(When ball struck by Hockey strick, it returns to its original position, means the direction of ball reverses. Hence $-ve$ sign of final velcoty).
$\therefore$ initial momentum $Pi=mu=0.1\times 10=1kgm/s$
and final momentum $\left(Pf\right)=mv=0.1\times -5=-0.5kgm/s$
Change in momentum $\left(△P\right)=Pf-Pi=-0.5-1=-1.5kgm/s$
Momentum is a vector quantity. The $-ve$ sign indicates the direction of momentum i.e. same as final velocity.