Problem 7-35 Work-energy theorem - B

A girl pulls a box of mass \(20.8\; kg\) across the floor. She is exerting a force on the box of \(95.6\; N\), inclined at \(35.0^\circ\) above the horizontal. The kinetic friction force on the box has a magnitude of \(75.5\; N\). Use the work-energy theorem to determine the speed of the box after being dragged \(0.750\; m\), assuming it starts from rest. [Ans. \(0.45\; m/s\)]

Accumulated Solution

FBD with all forces, directions and angles indicated.

One of the following is incorrect; which one?

(A)   \(\text{Work done = Change in}\; E_K\)

(B)   \(\sum F_d = \Delta ( ½ mv^2)\)

(C)   \(\sum F_d = \Delta E_K\)

(D)   \(\sum F_d = ½ m(v^2 - v_0{^2})\)

(E)   \(\sum F_d = ½ \;m(v - v_0)^2\)