Question

A boy of weight 400 N is moving on a straight level road against a friction of 6 N. After travelling a distance of 1.4 km he forgot the correct path at a round about of r = 100 m. He moves on the circular path for one and a half cycle and then he moves forward up to 1.4 km. Find the net work done by the boy against the friction.

Answer 1

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 a circular path. Therefore, as per the question statement the net displacement made by the boy will be,
S =1.4 km + diameter of the circular path about +1.4 km
$S=1.4\times {10}^{3}m$ + diameter of the circular path about + $1.4\times {10}^{3}m$
S =1400 m + 200m + 1400m
S =3000 m
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,
$W=6N\times 3000m$
W = 18000 N.m
W = 18000 Joule