Q. A force of $20N$ is applied on a body of mass $5\ kg$ resting on a horizontal plane. The body gains a kinetic energy of $10\ joule$ after it moves a distance $2\ m$. The frictional force is
A) $10\ N$
B) $15\ N$
C) $20\ N$
D) $30\ N$
Explanation
(b) Kinetic energy $= 10\ J$
$\Rightarrow \frac{1}{2}mv^{2} = 10 \Rightarrow v^{2} = 4$
From third equation of motion $v^{2} = u^{2} + 2as$
$4 = 0 + 2 \times a \times 2$
$\Rightarrow a = 1\ m/s^{2}$
$\because F_{s} = F - ma = 20 - 5 \times 1 = 15\ N$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.