Question

The block starts from rest as shown in the figure. Find the work done by force of $10\, N$ and friction in the time $0$ to $4\, \sec$. [Take $g =10\, m / s ^{2}$]

• A. 240 J ,-96 J
• B. 250 J , 96 J
• C. 240 J , 96 J
• D. 250 J ,-96 J

Answer 1

Answer: (A)

Here, applied force, $F=10\, N$

Friction force,
$f=\mu N=0.2 \times m g=0.2 \times 2 \times 10=4\, N$
Net force, $F_{\text {net }}=F-f=10-4=6\, N$
$\therefore $ Acceleration, $a=\frac{F_{\text {net }}}{m}$
$=\frac{6}{2}=3\, m s^{-2}$
Distance covered in $4\, s$,
$s=0+\frac{1}{2} a t^{2}=\frac{1}{2} \times 3 \times(4)^{2}=24\, m$
Work done by applied force of $10\, N$,
$W_{1}=F s=10 \times 24=240\, J$
Work done by friction force of $4\, N$,
$W_{2}=f s \cos 180^{\circ}=-4 \times 24=-96\, J$