Classical Mechanics
# Work

$\vec{F_1}$ and $\vec{F_2}$ acting on a box as the box slides rightward across a frictionless horizontal floor. Force $\vec{F_1}$ acts horizontally leftward with a magnitude of $4 \text{ N} .$ Force $\vec{F_2}$ is applied in a direction that makes a $60^\circ$ angle with the floor with a magnitude of $8 \text{ N}.$ The speed $v$ of the box at a certain instant is $6 \text{ m/s}.$ What is the net power acting on the box?

The figure above shows constant forcesA freight elevator is loaded with a cab with a total mass of $1200 \text{ kg},$ which is required to travel upward $18 \text{ m}$ in $100$ seconds, starting and ending at rest. The elevator's counterweight has a mass of only $1000 \text{ kg},$ so the elevator motor must help. With how much power must the motor do work to the cab?

The gravitational acceleration is $g= 10 \text{ m/s}^2.$