Question

A ball of mass 20 g is moving with a velocity of 40 $m{s}^{-1}$.On applying some constant force for 2 seconds it acquires a velocity of 80 $m{s}^{-1}$. What is the value of force?

• A. 1 N
• B. 0.6 N
• C. 0.4 N
• D. 1.5 N

Answer 1

The correct option is C

0.4 N

According to Newton's second law force is the ratio of change in momentum to time.

Given, Mass of the body $m$= 20 g = 0.02 kg , initial velocity(u) = 40 $m{s}^{-1}$ , final velocity(v) = 80 $m{s}^{-1}$ , Time(t) = 2 seconds.

Change in momentum $=mv-mu=m(v-u)=0.02(80-40)=0.8kgm/s$

$Force=\frac{changeinmomentum}{time}=\frac{0.8}{2}=0.4N$