Question

A body of mass 2 kg moving on a horizontal surface with an initial velocity of 4 m/sec comes to rest after 2 sec. If one wants to keep this body moving on the same surface with a velocity of 4 m/sec, the force required is

• A. 8 N
• B. 4 N
• C. Zero
• D. 2 N

Answer 1

The correct option is B

4 N

u=4 m/s, v=0, t= 2sec
v=u+at $\Rightarrow$ 0=4+2a $\Rightarrow a=-2m/s^2$
$\therefore$ Retarding force = ma =2 $\times$ 2= 4 N
This force opposes the motion. If the same amount of force is applied in forward direction, then the body will move with constant velocity.