Question

A boy of weight 400 N is moving on

a straight level road against a frictional forceof 6 N. After travelling a distance of 1.4 kmhe forgot the correct path at a round aboutof radius 100 m. However, he moves on thecircular path for one and half cycle and thenhe moves forward upto 1.4 km. Find the network done by the boy against the frictionalforce.

Answer 1

The question says that a boy of weight 400 N moves on a straight level road against the frictional force $F=6N$ and forgets the path and moves in circular path. Therefore, as per the question statement the net displacement made by the boy will be,
$$\begin{gathered} s=1.4km+\text{diameter of the circular path about}+1.4km \\ s=1.4\times {10}^{3}m+\text{diameter of the circular path about}+1.4\times {10}^{3}m \end{gathered}$$
that is,
$$\begin{gathered} s=1400m+200m+1400m \\ s=3000m \end{gathered}$$
Now, the net work done by the boy against the frictional force is,
$W=f\times s$
On substituting the values in the above equations we get,
$$\begin{gathered} W=6N\times 3000m \\ W=18000N.m \\ W=18000Joule \end{gathered}$$