3 min readβ’november 17, 2021

π Welcome to theΒ **AP Physics Unit 2 FRQ (Dynamics) Answers**.Β Have your responses handy as you go through the rubrics to see how you did!

β± Remember, the AP Physics 1 exam has 5 free-response questions, and you will be given 90 minutes to complete the FRQ section. (This means you should **give yourself ~18 minutes** to go through each practice FRQ.)

A worker pushes a wooden crate up a ramp at a constant velocity. The ramp has been covered with a material that when warm provides enough friction that it will not slide down the hill. When the ramp is exposed to the cold the coefficient of friction changes enough that the box will easily slide down the ramp.

(a) **Draw** a free body diagram for the box on the top dot and a free body diagram with components on the bottom dot. The dotted line represents the incline. (3pts)

- Replay: Free-Body Diagrams

(b) In the space provided below, **derive** an equation for the coefficient of friction, π, when the box is moving up the hill at constant velocity. Express your answer in terms of m, g, Fapp, trig identities, and π.

- Study Guide: Contact Forces

(c) If the mass of the box is 25 kg, the applied force is 250 N, and the angle π is 22o, **calculate** the coefficient of friction using your equation from part b) as the person is pushing the box up the hill. Show all work. (1pt)

(d) The ramp is now chilled until the coefficient of friction equals 0.02 and the box begins to accelerate down the incline. In addition, the person is no longer pushing the box. In the space provided below, **draw** a free body diagram for the box on the top dot and a free body diagram with components on the bottom dot. The dotted line represents the incline. (3pts)

- Replay: Typical Dynamics Problems

(e) **Derive** an equation for the acceleration of the box as it slides down the hill. Express your answer in terms of m, g, π, trig identities, and π. (4pts)

(f) **Calculate** the acceleration of the box down the hill using the information given in parts (a) through (e). Show all work. (2pts)

- π§ Want to continue reinforcing your knowledge of Unit 2? Check out Unit 2 Trivia, either
**as a document**or**as a game**.

- β Ready to move on to the next topic? Take a look at the collection of
**Unit 3 Resources**. - π Want to review multiple units? Check out all of the
**AP Physics 1 FRQs**. - π€ Got more questions? Want to help others studying the same topic? Jump into a room in
**Hours**!

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