Q: A block is pulled at an angle $$\theta$$ above the horizontal. Which equation gives the normal force on the block?

$$F_N = mg - F_{app} \sin\theta$$

Q: A block of mass $$m is on an $$inclined plane at angle $$\theta. $$The coefficient of kinetic friction is $$\mu_k. $$What is the acceleration of the block down the incline?

$$a = g(\sin\theta - \mu_k \cos\theta)$$

Q: A 5 kg block is pulled up a $$30^\circ$$ incline with a force of $$40\ \mathrm{N}. $$The coefficient of kinetic friction is $$0.3. $$What is the acceleration of the block? Use $$g = 10\ \mathrm{m/s^2$}.$$

$$a = \frac{40 - 5 \times 10 \sin 30^\circ - 0.3 \times 5 \times 10 \cos 30^\circ}{5}$$

Q: A block of mass $$m is $$pulled at an angle $$\theta$$ above the horizontal with force $$F. $$The coefficient of kinetic friction is $$\mu_k. $$Which equation gives the acceleration of the block?

$$a = \frac{F \cos\theta - \mu_k (mg - F \sin\theta)}{m}$$

Question 1

A car suddenly accelerates forward, causing a cup of coffee on the dashboard to spill backward, as shown in the image. Which of Newton's Laws best explains why the coffee appears to move backward?

Accepted Answer

Newton's First Law (Law of Inertia)

Question 2

A person is pushing a box across a rough surface, as shown in the image. If the box moves at a constant velocity, which statement is true about the forces acting on the box?

Accepted Answer

The applied force is equal to the friction force.

Question 3

Refer to the free body diagram shown (with $$F_N$$, $$F_{applied}$$, and $$mg). $$What is the direction of the acceleration if the box is moving to the right and speeding up?

Accepted Answer

To the right

Question 4

A cat is sitting on a table. According to Newton's Third Law, what is the reaction force to the table pushing up on the cat?

Accepted Answer

The cat pushing down on the table

Question 5

A sled is being pushed across an icy surface. The free body diagram includes $$F_N$$, $$mg$$, $$F_{applied}$$, and $$f_k. $$Which force is responsible for the sled's acceleration?

Accepted Answer

$$F_{applied}$$

Question 6

A block is pulled at an angle $$	heta$$ above the horizontal. Which equation gives the normal force on the block?

Accepted Answer

$$F_N = mg - F_{app} \sin	heta$$

Question 7

A 5 kg block slides down a frictionless incline at $$30^\circ. $$What is the acceleration of the block? Use $$g = 10\ \mathrm{m/s^2$}.$$

Accepted Answer

$$a = 10 \sin 30^\circ = 5\ \mathrm{m/s^2$}$$

Question 8

A 10 kg box is at rest on a horizontal surface. The coefficient of static friction is $$\mu_s = 0.4. $$What is the maximum force that can be applied horizontally before the box starts to move? Use $$g = 10\ \mathrm{m/s^2$}.$$

Accepted Answer

$$40\ \mathrm{N}$$

Question 9

A 0.5 kg toy car is initially at rest and reaches a velocity of $$2.4\ \mathrm{m/s} in$$ $$6\ \mathrm{s}. $$What is the net force acting on the car?

Accepted Answer

$$0.2\ \mathrm{N}$$

Question 10

A block of mass $$m is on an $$inclined plane at angle $$	heta. $$The coefficient of kinetic friction is $$\mu_k. $$What is the acceleration of the block down the incline?

Accepted Answer

$$a = g(\sin	heta - \mu_k \cos	heta)$$

Question 11

A 20 kg box is suspended by two ropes at angles $$\$$theta_1$$ = 40^\circ$$ and $$\$$theta_2$$ = 50^\circ$$ from the vertical. Which statement is true about the tensions $$T_1$$ and $$T_2$$?

Accepted Answer

$$T_1$$ \u003c $$T_2$$

Question 12

A spring with spring constant $$k = 100\ \mathrm{N/m} is $$stretched $$0.1\ \mathrm{m}$$ from equilibrium. What is the force exerted by the spring?

Accepted Answer

$$10\ \mathrm{N}$$

Question 13

Two identical springs, each with $$k = 4\ \mathrm{N/m}$$, are attached in parallel to a mass. What is the effective spring constant?

Accepted Answer

$$8\ \mathrm{N/m}$$

Question 14

A 5 kg block is pulled up a $$30^\circ$$ incline with a force of $$40\ \mathrm{N}. $$The coefficient of kinetic friction is $$0.3. $$What is the acceleration of the block? Use $$g = 10\ \mathrm{m/s^2$}.$$

Accepted Answer

$$a = \frac{40 - 5 	imes 10 \sin 30^\circ - 0.3 	imes 5 	imes 10 \cos 30^\circ}{5}$$

Question 15

A block of mass $$m is at $$rest on an incline. The coefficient of static friction is $$\mu_s. $$What is the minimum angle $$	heta at $$which the block will start to slide?

Accepted Answer

$$	heta = \arctan(\mu_s)$$

Question 16

A 10 kg box is suspended from a rope in an elevator accelerating upward at $$2\ \mathrm{m/s^2$}. $$What is the tension in the rope? Use $$g = 10\ \mathrm{m/s^2$}.$$

Accepted Answer

$$120\ \mathrm{N}$$

Question 17

A system consists of two blocks, $$m_1 on a $$table connected by a string over a pulley to $$m_2$$ hanging off the edge. If the table is frictionless, what is the acceleration of the system?

Accepted Answer

$$a = \frac{m_2$ g}{m_1$ + m_2$}$$

Question 18

A block of mass $$m is $$pulled at an angle $$	heta$$ above the horizontal with force $$F. $$The coefficient of kinetic friction is $$\mu_k. $$Which equation gives the acceleration of the block?

Accepted Answer

$$a = \frac{F \cos	heta - \mu_k (mg - F \sin	heta)}{m}$$

AP Physics C Mechanics: Dynamics, Forces, Friction, Equilibrium, and Springs

Study Guide - Practice Questions

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