Unit 5: Torque and Rotational Dynamics
Physics C: Mech · Unit 5 · Paper 2

Torque and Rotational Dynamics unit test

A test on this unit alone, marked as a percentage and a letter grade — for the test your class is actually sitting, rather than for May. Answer everything, then submit once: seeing the answer to question 3 before attempting question 4 makes the final percentage meaningless.

Paper 1Paper 2Paper 3
Each paper is built from this unit’s 38 terms and is the same for everyone, so a teacher can assign “Unit 5, Paper 2” and every student sits the identical test. Multiple choice is marked objectively; the written sections you mark yourself against the model answer and rubric.
Suggested time 37 min 34 points0/17 attempted
1

Moments of inertia add

2

Rod about one end

3

Standard moments of inertia

4

Spherical shell

5

Solid disk or cylinder about its axis

6

The rotational kinematic equations

7

Equilibrium of a leaning ladder

8

Moment of inertia of a point mass

9

Moment of inertia by integration

10

Torque about different axes

11

Direction of friction in rolling

12

Solid sphere

Short answer 1. Define or explain: Rolling without slipping

3 pts

Short answer 2. Define or explain: Rotational equilibrium

3 pts

Short answer 3. Define or explain: Slipping vs rolling

3 pts

Short answer 4. Define or explain: Perpendicular-axis theorem

3 pts

Free response

10 pts

Students are asked to determine the rotational inertia of a uniform disk that is free to rotate about a fixed horizontal axle through its center. A light string is wrapped around a spool of radius R = 0.050 m attached to the disk, and a hanging block of mass m is attached to the free end. The students release the block from rest and measure its acceleration for several different masses. m (kg) 0.10 0.20 0.30 0.40 0.50 a (m/s²) 1.96 3.27 4.20 4.90 5.44 Friction in the axle is negligible.

A(i). Describe a procedure the students could use to measure the acceleration of the block. A(ii). Describe one step that would reduce experimental uncertainty.

B(i). Derive an expression relating the acceleration of the block to the hanging mass m, the spool radius R, and the rotational inertia I of the disk. B(ii). Indicate what quantities the students should graph on the axes to obtain a straight line usable to determine I.

C(i). Calculate the values to be plotted on each axis. C(ii). Describe the axis labels, with units, and the positions of the plotted points, and describe the best-fit line.

D. Using the best-fit line described in part C, calculate an experimental value for the rotational inertia of the disk.