Question

A $120g$ mass has a velocity $\overrightarrow{v}=2\hat{i}+5\hat{j}m{s}^{-1}$ at a certain instant. Its kinetic energy is:

• A. $3J$
• B. $4J$
• C. $5J$
• D. $1.74J$

Answer 1

The correct option is D $1.74J$

Here, $m=120g=120\times {10}^{-3}kg=0.12kg$

$\overrightarrow{v}=2\hat{i}+5\hat{j}m{s}^{-1}$

$\therefore v^2=\overrightarrow{v}.\overrightarrow{v}$

$=(2\hat{i}+5\hat{j}).(2\hat{i}+5\hat{j})$

$=4+25=29m^2{s}^{-2}$

Kinetic energy, $K=\frac{1}{2}m.v^2$
$=\frac{1}{2}\times 0.12kg\times \left(29m^2{s}^{-2}\right)=1.74J$.