Problem 7-62 Energy cons. with friction - C

A pen of mass $0.057 \;kg$ is sliding across a horizontal desk. In sliding $25 \;cm$, its speed decreases to $5.7 \;cm/s$. What was its initial speed if the force of kinetic friction exerted on the pen by the desk is $0.15\; N$ in magnitude? Use conservation of energy.

Correct

Friction is acting so some mechanical energy is lost as thermal energy.

In this problem:

(A)   Potential energy changes.

(B)   Kinetic energy changes.

(C)   Both potential and kinetic energies change.