AP Physics C: Mechanics / Unit 3: Work, Energy, and Power
3.4 Conservation of Energy
Notes
If only conservative forces (gravity, springs) do work, mechanical energy is conserved: $K_i+U_i=K_f+U_f$.
- Friction turns mechanical energy into thermal energy.
Practice
A ball dropped from 5 m (no air resistance) hits the ground at (g = 10):
$\displaystyle v=\sqrt{2gh}=\sqrt{100}$.
A roller coaster starts at rest at the top. Its speed is greatest:
Most $U$ turned into $K$.
With friction, the total energy of the universe:
Energy is never destroyed.
A mass slides down a frictionless curved track from height $h$. Its speed at the bottom:
Only height matters.
Ready for more? Take the Unit 3 test.