Unit 2: Force and Translational Dynamics
Physics C: Mech · Unit 2 · Paper 3

Force and Translational 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 59 terms and is the same for everyone, so a teacher can assign “Unit 2, Paper 3” 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

Static friction as an inequality

2

Newton's first law and inertial frames

3

Impulse from a variable force

4

Ideal pulley

5

Terminal velocity from a drag law

6

Terminal velocity for linear drag

7

The spring force as a restoring force

8

Time constant of linear drag

9

The normal force is not always mg

10

Solving the terminal velocity differential equation

11

Tension in an ideal string

12

Modified Atwood machine

Short answer 1. Define or explain: Coefficients of friction are dimensionless

3 pts

Short answer 2. Define or explain: Stacked blocks with friction

3 pts

Short answer 3. Define or explain: Weight versus mass

3 pts

Short answer 4. Define or explain: Newton's third law pairs

3 pts

Free response

10 pts

A ball of mass m is released from rest and falls vertically through a fluid. In addition to gravity, the ball experiences a resistive force of magnitude bv directed opposite its velocity, where b is a positive constant and v is the ball's speed. Take downward as positive.

A. Write, but do not solve, a differential equation that describes the ball’s velocity as a function of time.

B. Derive an expression for the terminal speed of the ball, in terms of m, b and physical constants.

C. Solve the differential equation from part A to obtain an expression for the ball’s speed as a function of time, in terms of m, b, t and physical constants.

D. Determine an expression for the ball’s acceleration at the instant it is released, and use your result from part C to justify that your expression for v(t) is consistent with it.