Problem 7-62 Energy cons. with friction - Part 2 - B

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.

FBD with all forces and directions indicated.


Only the \(KE\) changes in this problem.

The expression for \(KE\) is:

(A)   \(mgh\)

(B)   \(mv\)

(C)   \((1/2)mv^2\)