7-62. 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.