# Problem 7-62 Energy cons. with friction - Part 3 - 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.

Accumulated Solution

$E_K = (1/2)mv^2$

Correct

The energy converted to heat is:

(A)   Unknown since we are not given the coefficient of friction.

(B)   Equal to the work done against the friction force.

(C)   Equal to the initial kinetic energy.