Question

A body of mass $2 \, kg$ moving on a horizontal surface with an initial velocity of $4 \, m \, s^{- 1}$ comes to rest after $2 \, s$ . If one wants to keep this body moving on the same surface with a velocity of $4 \, m \, s^{- 1}$ the force required is

• A. $8 \, N$
• B. $4 \, N$
• C. Zero
• D. $2 \, N$

Answer 1

Answer: (B)

$u=4m / s , \, v=0, \, t=2 \, sec$
$v=u+at \, \Rightarrow \, 0=4+2a \, \Rightarrow \, a=-2m / s^{2}$
$\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.