Energy and Momentum of Rotating Systems practice quiz

Key ideaK_rot = ½Iω², and work by a torque is ∫τ dθ.

Common mistakeLeaving out ½Iω² for a pulley or a rolling object.

Key ideaL = Iω for a rigid body, and L = r × p for a particle. Net torque = dL/dt.

Common mistakeTaking the angular momentum about a different point than the one used for the torques.

Key ideaWith no net external torque about a point, the angular momentum about that point is constant, even during a collision.

Common mistakeConserving linear momentum when a pivot exerts a force, or conserving kinetic energy in an inelastic rotational collision.

Key ideaRolling without slipping links v = Rω and a = Rα. Static friction does no work on a rolling object.

Common mistakeThinking friction removes energy from an object rolling without slipping.

Key ideaFor an orbit, gravity provides the centripetal force. Angular momentum about the planet is conserved, and the total energy is negative for a bound orbit.

Common mistakeUsing U = mgh far from the planet, where U = −GMm/r is needed.