Problem 7-65 Energy cons. with friction - Part 2 - A

A box of apples (mass \(22\; kg\)) slides down a ramp inclined at \(44^\circ\) to the horizontal. The fiction force on the box has a magnitude of \(79\; N\). If the box starts from rest and slides \(2.5\; m\) along the ramp, determine:

(a) the work done by friction
(b) the box's final kinetic energy (using conservation of energy)
(c) the thermal energy produced.

[Ans. (a) \(-2.0\times 10^2 \;J\)   (b) \(1.8\times 10^2\; J\)   (c) \(2.0\times 10^2\; J\) ]

Accumulated Solution

FBD with all angles and forces indicated.

\(W_f = fd\)


The work done by friction is:

(A)   \((79 \;N)(2.5\; m) = 2.0\times 10^2\; N\)

(B)   \((-79\; N)(2.5 \;m) = -2.0\times 10^2\; N\)