Question

A body accelerates uniformly from rest to a velocity of $1\, ms ^{-1}$ in $15$ second. The kinetic energy of the body will be $\frac{2}{9} J$ when $' t '$ is equal to [Take mass of body as $1\, kg ]$

• A. 4 s
• B. 8 s
• C. 10 s
• D. 12 s

Answer 1

Answer: (C)

$a=\frac{v-u}{t}=\frac{1-0}{15}=\frac{1}{15} m / s ^{2}$
$\Rightarrow v=\left(\frac{1}{15}\right) t$
$K=\frac{1}{2} m v^{2} ; \frac{2}{9} J$
$=\frac{1}{2}(1 kg )\left(\frac{1}{15} t \frac{ m }{ s }\right)^{2}$
$\frac{2}{9}=\frac{1}{2} \cdot \frac{1}{15^{2}} \cdot t^{2} ; t^{2}$
$=\frac{15^{2} \times 2^{2}}{9}$
$\Rightarrow t=\frac{15 \times 2}{3}=10 \,s$.