AP Physics 1 2020 Exam Sample Questions (pdf)

AP Physics 2020 Exam SAMPLE Question 1

(Adapted from: AP Physics 1 Course and Exam Description FRQ 1)

Allotted time: 25 minutes (+ 5 minutes to submit)

A small sphere of mass M is suspended by a string of length L. The sphere is made
to move in a horizontal circle of radius R at a constant speed, as shown above. The
center of the circle is labeled point C, and the string makes angle θ_{0} with the vertical.

Two students are discussing the motion of the sphere and make the following
statements.

Student 1: None of the forces exerted on the sphere are in the direction of
point C, the center of the circular path. Therefore, I don’t see how there can
be a centripetal force exerted on the sphere to make it move in a circle.

Student 2: I see another problem. The tension force exerted by the string is
at an angle from the vertical. Therefore, its vertical component must be
less than the weight Mg of the sphere. That means the net force on the
sphere has a downward vertical component, and the sphere should move
downward as well as moving around in a circle.

(a) What is one aspect of Student 1’s reasoning that is incorrect? Explain why.

(b) What is one aspect of Student 2’s reasoning that is incorrect? Explain why.

Student 3 correctly derives the equations
to relate the tension force F_{T} to the net force F_{net} and the other quantities.

(c) Explain how one of the equations can be used to challenge Student 1’s claim.

(d) Explain how one of the equations can be used to challenge Student 2’s claim.

The students observe that the radius R increases as the speed v of the sphere
increases. Together, they derive the equation to calculate the radius of
the circle R followed by the sphere if its speed is v.

(e) Regardless of whether this equation is correct or incorrect, does it plausibly
model the students’ observation about the relationship between R and v?
Why or why not?

(f) This equation does not correctly model the relationship between R and v if
v is very fast. Explain why.

Instead of moving in a horizontal circle, the sphere now moves in a vertical plane
so that it is a simple pendulum, as shown above. The maximum angle θ_{max} that the
string makes from the vertical can be assumed to be small. The graph below shows
data for the square of the pendulum period T as a function of string length L.
Explain how the above graph would change under each of the following
circumstances. Justify your answers.

(g) The mass of the sphere is increased.

(h) The maximum angle θ_{max} is decreased.

(i) The pendulum is taken to the Moon.

(j) The graph above shows the angle theta from the vertical as a function
of time for the pendulum. Explain how this graph shows evidence of a
net force acting on the sphere, and how it shows that this net force is a
restoring force.

As the sphere swings back and forth, it must also rotate a small amount during
each swing. The figures below indicate the direction that the sphere rotates as it is
swinging in each direction.

(k) In order for the sphere’s rotation to change direction, a torque must be
exerted on the sphere. When the sphere is at its maximum rightward
displacement, what is the direction (clockwise or counterclockwise) of
the torque exerted on the sphere with respect to the point of attachment
between the sphere and string? Briefly state why the torque is in the
direction you indicated.

AP Physics 2020 Exam SAMPLE Question 2

(Adapted from: AP Physics 1 Course and Exam Description FRQ 2)

Allotted time: 15 minutes (+ 5 minutes to submit)

A spring with unstretched length L_{1} is hung vertically, with the top end fixed in
place, as shown in Figure 1 above. A block of mass M is attached to the bottom of
the spring, as shown in Figure 2, and the spring has length L_{2} > L_{1}
when the block hangs at rest. The block is then pulled downward and held in place so that the
spring is stretched to a length L_{3} > L_{2}, as shown in Figure 3.

The student releases the block. Consider the time during which the block is moving
upward toward its equilibrium position and the spring length is still longer than L_{2}.
Indicate whether the total mechanical energy is increasing, decreasing, or constant
for each of the systems listed below and explain why.

(a) System 1: The block (energy E1)

(b) System 2: The block and the spring (energy E2)

(c) System 3: The block and the Earth (energy E3)

(d) The block is released at time t = 0. The length of the spring is shown in the
graph above as a function of time. During which interval(s), if any, is the
weight force acting on the block greater than the spring force acting on the
block? Explain your reasoning.

(e) When the block reaches its lowest point after oscillating several times, the
student attaches a new block of mass m < M to the block of mass M without
exerting any noticeable force to the block of mass M or changing the energy
stored in the spring at that instant. In a clear, coherent, paragraph-length
response that may reference equations, explain how the graph of length vs.
time will change and why.

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