Question

A man pushes a $10kg$ box at a constant velocity over a distance of $4m$ on a rough horizontal surface. The coefficient of kinetic friction between the box and the floor is $0.3$. Calculate the work done by the person on the box?

• A. $12J$
• B. $40J$
• C. $75J$
• D. $120J$
• E. $400J$

Answer 1

Answer: (D)

$120J$

Given : $m=10kg$ $\mu =0.3$ $S=4$ m

As the velocity of the box is constant, thus net force acting on the box must be equal to zero.

$\therefore$ Horizontal force applied by man $F=f={\mu }_{k}mg=0.3\times 10\times 10=30$ $N$

Thus work done by man $W=|F||S|cos\theta$

$\therefore$ $W=30\times 4\times cos{0}^o=120$ J