Question

A body of mass $2\, kg$ starts from rest and moves with uniform acceleration. It acquires a velocity $20\, m\, s^{-1}$ in $4\, s$. The power exerted on the body in $2\, s$ in watts is

• A. $50$
• B. $100$
• C. $150$
• D. $200$

Answer 1

Answer: (B)

Let a body moves with uniform acceleration a. From $v = u + at$
Here, $u = 0, v = 20\, m \,s^{-1}, t = 4 \,s$
$\therefore a=\frac{\upsilon-u}{t}=\frac{20-0}{4}=5\,m$
Force exerted on the body,
$F = m × a = \left(2 \,kg\right) \left(5 \,m\, s^{-2}\right) = 10 \,N$
Velocity acquired by the body in $2\, s$ is
$\upsilon=\left(5\,m\,s^{-2}\right)\left(2\,s\right)=10\,m\,s^{-1}$
The power exerted on the body in $2\,s$ is
$P=F\upsilon=\left(10\,N\right)\left(10\,m\right)=100\,W$