Q. A body of mass 4 kg is moving with momentum of $8\ kg - ms^{- 1}$. A force of 0.2 N acts on it in the direction of motion of the body for 10 s. The increase in KE in joule is
A) 10
B) 8.5
C) 4.5
D) 4
Explanation
(c) Initially, $4u = 8 \Rightarrow u = 2m/s$
Now, $mv - mu = Ft$
$mv - 8 = 0.2 \times 10$
or $v = 5/2\ ms^{- 1}$
Increase in KE $= \frac{1}{2}m(v^{2} - u^{2})$
$= \frac{1}{2} \times 4\left\lbrack \left( \frac{5}{2} \right)^{2} - (2)^{2} \right\rbrack$
$= 4.5\ J$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.