Question

A force acting on an object of mass 500gm changes its speed from 200 cm/s to
0.2 m/s. The change in momentum is?

• A. Increase by 0.90 Ns
• B. Decrease by 0.90 Ns
• C. Increase by 90 g cm/s
• D. Decrease by 90 g cm/s
  

Answer 1

The correct option is B Decrease by 0.90 Ns

$\Delta p$ is the change in momentum
Let us find out initial momentum
$p_i=M{v}_{initial}$
$=500\times 200gcm/s$$=\frac{500}{1000}\times 2kgm/s$
$p_i=1kgm/s$
Next, let us find final momentum
$p_f=\frac{500}{1000}\times 0.2$$=0.1kgm/s$
So change in momentum will be
$\Delta p=p_f-p_i=0.1-1$
$=-0.9kgm/s$
$=-0.9Ns$(-ve sign indicates decrease in momentum)