Question

A body of mass 5 kg at rest is under the action of a force which gives it a velocity given by $v=3t$ m/s, here $t$ is time in seconds. The work done by the force in two seconds will be:

• A. $90J$
• B. $45J$
• C. $180J$
• D. $30J$

Answer 1

The correct option is A $90J$

$F=m\frac{dv}{dt}=3\times 5=15N$ $ds=3t.dt$

Work done: $W=\int F.ds$ $={\int }_0^{2}15.3t.dt$ $=\frac{45\times 4}{2}=90J$