Torque and Work AP Physics 1 FRQ – Exam Style Questions etc.
Torque and Work AP Physics 1 FRQ
Unit 6: Energy and Momentum of Rotating Systems
Weightage : 10-15%
Exam Style Practice Questions, Torque and Work AP Physics 1 FRQ
Question: (7 points, suggested time 13 minutes)
Identical blocks 1 and 2 are placed on a horizontal surface at points A and E, respectively, as shown. The surface is frictionless except for the region between points C and D, where the surface is rough. Beginning at time At , block 1 is pushed with a constant horizontal force from point A to point B by a mechanical plunger. Upon reaching point B, block 1 loses contact with the plunger and continues moving to the right along the horizontal surface toward block 2. Block 1 collides with and sticks to block 2 at point E, after which the two-block system continues moving across the surface, eventually passing point F.
(a) On the axes below, sketch the speed of the center of mass of the two-block system as a function of time, from time tA until the blocks pass point F at time tF . The times at which block 1 reaches points A through F are indicated on the time axis.
(b) The plunger is returned to its original position, and both blocks are removed. A uniform solid sphere is placed at point A, as shown. The sphere is pushed by the plunger from point A to point B with a constant horizontal force that is directed toward the sphere’s center of mass. The sphere loses contact with the plunger at point B and continues moving across the horizontal surface toward point E. In which interval(s), if any, does the sphere’s angular momentum about its center of mass change? Check all that apply.
____ A to B ____ B to C ____ C to D ____ D to E _____ None
Briefly explain your reasoning.
Answer/Explanation
Ans:
(a)
(b)
__√___ C to D
A change in angular momentum means that the sphere has a torque being applied to it over a period of time, (L = tot), a torque is not applied from A to B because the force is directed towards the center of mass, since the surface is frictionless at B to C and D to E, there is no force that is applied to the sphere, and therefore no torque A torque is only applied during the interval from C to D, since the surface is rough, which means that friction exist. The force of friction applied a torque to the sphere causing the angular momentum to change at C to D.