Question

A body of mass $10\, kg$ is acted upon by a force given by equation $F=\left(3 t^{2}-30\right)$ newtons. The initial velocity of the body is $10 \,m / s$. The velocity of the body after $5 \,s$ is

• A. 4.5 m / s
• B. 6 m / s
• C. 7.5 m / s
• D. 5 m / s

Answer 1

Answer: (C)

Body is acted upon by a force given by equation
$F=\left(3 \,t^{2}-30\right) N$
$\therefore m(v-u)=\int F d t$
$=\frac{3 \,t^{3}}{3}-30\, t=t^{3}-30\, t $
$ =5^{3}-30(5)=125-150=-25 $
$\therefore m[v-10]=-25$
$\Rightarrow $ Final velocity $v=7.5\, m / s$