Energy Empire: Hill Roller
Kinetic KGravitational Ug (or work by gravity)Internal energy (or work by friction)
PREDICT
ZERO LINE:
How this connects to AP Physics 1 (Topics 3.3 and 3.4): gravitational potential energy depends on a zero line you choose, but its change does not. Mechanical energy is conserved for the cart-plus-Earth system only when no external force does work and nothing becomes internal energy. Friction turns mechanical energy into internal energy (Edis = f·d). Choose "cart alone" and gravity becomes an external force that does work, so K = Wgravity + Wfriction. Friction here is μmg cosθ, so it dissipates μmg for every horizontal metre travelled.