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

Answer: (B)

4 N

Answer 2

$u = 4\mspace{6mu} m/s$, $v = 0,\mspace{6mu} t = 2\sec$

$v = u + at$ ⇒ $0 = 4 + 2a$ ⇒ $a = - 2m/s^{2}$

$\therefore$ 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.