Question

A body of mass $5kg$ is moving with a momentum of $10kgm/s.$ A force of $0.2N$ acts on it in the direction of motion of the body for $10s$.The increase in its kinetic energy is

• A. $2.8J$
• B. $3.2J$
• C. $3.8J$
• D. $4.4J$

Answer 1

Answer: (D)

$4.4J$

Given , $m=5kg,p=10kg-m/s$,
$F=0.2N$
and $t=10s$
Let initial momentum be p
$p=mu$
$10=5u$
$\Rightarrow$ $u=2m/s$
From Newton's 2nd law
Acceleration $a=\frac{F}{m}$
$=\frac{0.2}{5}=0.04m/s^2$
Final velocity $v=u+at$
$=2+0.04\times 10$
$=2.4m/s$
Increase in $KE=\frac{1}{2}m(v^2-u^2)$
$=\frac{1}{2}\times \left[\right(2.4{)}^2-\left(2{)}^2\right]$
$=4.4J$