Question

The figure shows three forces applied to a trunk that moves leftward by 2.84 m over a frictionless floor. The force magnitudes are F₁ = 5.19 N, F₂ = 9.16 N, andF₃ = 2.82 N, and the indicated angle is θ = 60°. (a) During the displacement, what is the net work done on the trunk by the three applied forces, the gravitational force, and the normal force? (b) Is there a net transfer of energy to or from the trunk? (c) Does the kinetic energy of the trunk increase or decrease?

Answer 1

If the floor is frictionless, the downward forces do not do anything. The trunk is heavy enough not to be effected.F1 and f2 are the main forces in this problem. The upward force (vertical component) is partially offset by F3 but the difference (F2*Sin(60) - F3 = 9.16sin60 - 2.82 = 5.11 ) on a frictionless surface and moving a trunk is not going to matter.

F2 has a horizontal component. F2*cos(60) = 9.16*0.5 = 4.6

F1 is moving left so likely this whole system is going left. The net force left is 5.11 - 4.6 = 0.5N

A]
Work = F*d = 0.5N*2.84 meters = 1.42 J

B]
It should increase, especially if the trunk started from 0. The work has to be dissipated somehow. There are no other forces opposing its motion, so the trunk will increase in velocity which increases its KE.