Question

A force of $10N$ acts on a $5kg$ body initially at rest. The work done by the force during the first two seconds of motion of the body is

• A. $30J$
• B. $40J$
• C. $20J$
• D. $80J$

Answer 1

The correct option is A $30J$

Force, $F=10N$

Mass, $m=5Kg$

Force,

$F=ma$

$a=2m/s^2$

Work done, $W=F.ds$

In first second, displacement,

$s=\frac{1}{2}a{t}^2$

$s=\frac{1}{2}\times 2\times 1$

$s=1m$

So, work done,$W=10\times 1=10J$

In second second, $s=\frac{1}{2}\times 2\times 4=4m$

So, the displacement is , $4-1=3m$

Hence, work done in 2 second is,

$W=10\times 3$

$W=30J$