AP Physics 1 2.2 Forces and Free-Body Diagrams

Figure for Question 2.2 Forces and Free-Body Diagrams question 1 — AP Physics 1: Algebra-Based

(12 points, suggested time 25 minutes) A student in a physics lab has a block with a fan attached to it, as shown in the figure above. The fan has a pivot so that the angle $\theta$ it makes with the horizontal can be adjusted between 0° and 90°. When the fan is pointed horizontally so that $\theta=0^{\circ}$ , the block accelerates from rest along a track, even though there is friction between the block and the track. For the following questions, assume that the student has access to equipment that would usually be found in a school physics laboratory.

(a)

Figure for Question (a) — AP Physics 1: Algebra-Based

(a) Describe an experimental procedure that the student could use to measure the force F that the air exerts on the fan-block system when the fan is turned on. Assume that the magnitude of this force is the same for all angles $\theta$ .

[ 3 ]

(i)

Figure for Question (i) — AP Physics 1: Algebra-Based

i. What quantities would be measured?

(ii)

Figure for Question (ii) — AP Physics 1: Algebra-Based

ii. What equipment would be used for the measurements, and how would that equipment be used? Include a labeled diagram of the experimental setup.

(iii)

Figure for Question (iii) — AP Physics 1: Algebra-Based

iii. Describe the overall procedure to be used. Give enough detail so that another student could replicate the experiment.

(iv)

Figure for Question (iv) — AP Physics 1: Algebra-Based

iv. Describe how the force can be determined from the measurements described in parts (a)i-iii.

(b)

Figure for Question (b) — AP Physics 1: Algebra-Based

(b) Describe an experimental procedure that would allow the student to use the fan-block system, with the fan turned on, to find the coefficient of kinetic friction between the block and the track.

[ 3 ]

(i)

iv. On the dot to the right, which represents the fan-block system, draw and label the forces (not components) that are exerted on the system during the experiment described in parts (b)i-iii. Represent each force by a distinct arrow starting on, and pointing away from, the dot.

[Maximum number: 3]

Figure for Question 2.2 Forces and Free-Body Diagrams question 2 — AP Physics 1: Algebra-Based

(12 points, suggested time 25 minutes)
This problem explores how the relative masses of two blocks affect the acceleration of the blocks. Block A, of mass $m_{A}$ , rests on a horizontal tabletop. There is negligible friction between block A and the tabletop. Block B, of mass $m_{B}$ , hangs from a light string that runs over a pulley and attaches to block A, as shown above. The pulley has negligible mass and spins with negligible friction about its axle. The blocks are released from rest.

Now suppose neither block's mass is much greater than the other, but that they are not necessarily equal. The dots below represent block A and block B, as indicated by the labels. On each dot, draw and label the forces (not components) exerted on that block after release. Represent each force by a distinct arrow starting on, and pointing away from, the dot.

LO 3.A.2.1, SP 1.1; LO 3.A.3.1, SP 6.4 3 points
Now suppose neither block's mass is much greater than the other, but that they are not necessarily equal. The dots below represent block A and block B, as indicated by the labels. On each dot, draw and label the forces (not components) exerted on that block after release. Represent each force by a distinct arrow starting on, and pointing away from, the dot.

Figure for Answer to Question 2.2 Forces and Free-Body Diagrams question 2 — AP Physics 1: Algebra-Based

For a correct normal force on block A with acceptable label: $N, F_{\mathrm{N}}$ , "normal force,"
$F_{\text {table }}$ , "table force," or any other label indicating the force is "normal" or comes
from the table

1 point

For correct gravitational forces with acceptable label on both diagrams: $F_{\mathrm{g}}, F_{\text {grav }}, W$ ,
$m g, m_{\mathrm{A}} g$ , "gravity," "grav force," but NOT G or g, and no extraneous forces on
either diagram

1 point

For correct tension forces with acceptable label on both diagrams: "tension," "string
force," $F_{T}, F_{\text {tension }}, F_{\text {string }}, F_{S}, T$ , or some other label indicating that the force
comes from the string or from tension. NOT acceptable: $m_{B} g, F_{m_{B}}$ , "force from
block B" or other indications that the force is "created" by block B1 point

AP Physics 1 2.2: Forces and Free-Body Diagrams

Exam points

Covered syllabus points

Covered syllabus points

2.2 Forces and Free-Body Diagrams question 1

Question (a)

Question (i)

Question (ii)

Question (iii)

Question (iv)

Question (b)

Question (i)

2.2 Forces and Free-Body Diagrams question 2