Question

Certain force acting on a 20 kg mass changes its velocity from $5m{s}^{-1}$ to $2m{s}^{-1}$. Calculate the work done by the force.

• A. $-210J$.
• B. $210J$.
• C. $-105J$.
• D. $420J$.

Answer 1

The correct option is A $-210J$.

Given, $mass,{}^{\prime }m=20kg$;
$initialvelocity,u=5m{s}^{-1}$;
$finalvelocity,v=2m{s}^{-1}$
$Workdonebytheforce=changeinkineticenergy$

or $W=\frac{1}{2}m{v}^2-\frac{1}{2}m{u}^2=\frac{1}{2}m(v^2-u^2)$

or $W=\frac{1}{2}\left(20\right)\left[\right(2{)}^2-\left(5{)}^2\right]=-210J$.