Two identical uniform solid cylinders, Cylinder X and Cylinder Y
PHYSICS · Multi-part · AP · Physics 1: Algebra-based · Energy and Momentum of Rotating Systems · Energy and Momentum of Rotating Systems
Problem
Two identical uniform solid cylinders, Cylinder X and Cylinder Y, roll from left to right across the same horizontal floor. Five equally-spaced stroboscopic flashes capture their motion. For each cylinder, the flashes show both the position of the center of mass and a small dot painted on the rim.
• For Cylinder X, each successive flash shows the dot making contact with the floor at the instant of the flash, and the horizontal spacing between successive center-of-mass images is constant.
• For Cylinder Y, the dot touching the floor during one flash is seen somewhere on the side of the rim (not at the floor) in the next flash, even though the horizontal center-of-mass spacing between flashes is again constant.
Answer the following questions about the motion of the two cylinders.
(a) For each cylinder, indicate whether its motion is pure rolling, rolling with slipping, or pure sliding. Support your identifications with specific evidence from the stroboscopic descriptions.
(b) For the cylinder that is rolling with slipping, state whether the floor exerts static or kinetic friction. Explain how the observed motion of the painted dot leads to your choice.
(c) Compare the mechanical energy of Cylinder X to that of Cylinder Y after five flashes. Assume both cylinders have the same mass and radius. Justify your answer qualitatively without using numerical calculations.