Problem 7-62 Energy cons. with friction - A
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.
No. External forces (friction) act so momentum is NOT conserved.