A man wishes to pull a crate 15m across a rough floor by exerting a force of 100 N. The

coefficient of kinetic friction is 0.25. For the man to do the least work, the angle between the

force and the horizontal should be:

A. 0

B. 14?

C. 43?

D. 66?

E. 76?

option (E) is correct.

Explanation:

Work done is defined as the product of force and the distance in the direction of force.

force, f = 100 N

Coefficient of friction, = 0.25

distance = 15 m

So, net force F = f - friction force

F = 100 - 0.25 x m g

Work = (100 - 0.25 mg) x d cosθ

For minimum work, the angle should be maximum.

So, the value of θ is 76°.

thus, option (E) is correct.