Q: A 5 kg box is pulled horizontally across a rough surface with a constant velocity. The pulling force is 30 N. What is the magnitude of the frictional force acting on the box?

$$F_{\text{friction}} = 30\ \text{N}$$

Q: A 10 kg crate is at rest on a horizontal floor. The coefficient of static friction between the crate and the floor is $$\mu_s = 0.4. $$What is the maximum horizontal force that can be applied before the crate starts to move?

$$F_{\text{max}} = 40\ \text{N}$$

Q: A person stands on a scale in an elevator accelerating upward at $$a. If $$the person's mass is $$m$$, what is the apparent weight?

$$W_{\text{apparent}} = m (g + a)$$

Q: A 3 kg object is acted upon by two forces: $$F_1 = 10$$\ \text{N}$$ to the right and F_2$ = 4\ \text{N} to $$the left. What is the acceleration of the object?

$$a = 2\ \text{m/s}^2$$\ to the right

Q: A block slides down an inclined plane with angle $$\theta$$ and coefficient of kinetic friction $$\mu_k. $$Which equation gives the acceleration $$a of $$the block?

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

Q: A 1 kg object moves in a circle of radius 2 m with a period $$T = 4 s. $$What is its speed?

$$v = \frac{2 \pi r}{T} = \frac{4 \pi}{4} = \pi\ \text{m/s}$$

Question 1

A 5 kg box is pulled horizontally across a rough surface with a constant velocity. The pulling force is 30 N. What is the magnitude of the frictional force acting on the box?

Accepted Answer

$$F_{	ext{friction}} = 30\ 	ext{N}$$

Question 2

A car of mass $$m is $$moving in a circle of radius $$r at $$constant speed $$v. $$What is the net force acting on the car, and in which direction does it point?

Accepted Answer

$$F = \frac{m v^2$}{r}$$; toward the center of the circle

Question 3

A 2 kg object is suspended from a rope and remains at rest. What is the tension in the rope?

Accepted Answer

$$T = 19.6\ 	ext{N}$$

Question 4

A 10 kg crate is at rest on a horizontal floor. The coefficient of static friction between the crate and the floor is $$\mu_s = 0.4. $$What is the maximum horizontal force that can be applied before the crate starts to move?

Accepted Answer

$$F_{	ext{max}} = 40\ 	ext{N}$$

Question 5

A satellite orbits Earth in a circular orbit of radius $$r. $$Which equation gives the speed $$v of $$the satellite?

Accepted Answer

$$v = \sqrt{\frac{G M}{r}}$$

Question 6

A person stands on a scale in an elevator accelerating upward at $$a. If $$the person's mass is $$m$$, what is the apparent weight?

Accepted Answer

$$W_{	ext{apparent}} = m (g + a)$$

Question 7

Two ice skaters push off from each other. If skater A has mass $$m_A$$ and skater B has mass $$m_B$$, which statement best describes the forces they exert on each other?

Accepted Answer

Both skaters exert equal and opposite forces on each other

Question 8

A 3 kg object is acted upon by two forces: $$F_1 = 10$$\ 	ext{N}$$ to the right and F_2$ = 4\ 	ext{N} to $$the left. What is the acceleration of the object?

Accepted Answer

$$a = 2\ 	ext{m/s}^2$$\ to the right

Question 9

A block slides down an inclined plane with angle $$	heta$$ and coefficient of kinetic friction $$\mu_k. $$Which equation gives the acceleration $$a of $$the block?

Accepted Answer

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

Question 10

A planet of mass $$m$$ orbits a star of mass $$M at a $$distance $$r. $$What is the gravitational force between them?

Accepted Answer

$$F = \frac{G m M}{r^2$}$$

Question 11

A 6 kg object is at rest on a table. What is the normal force acting on the object?

Accepted Answer

$$N = 58.8\ 	ext{N}$$

Question 12

A 2 kg ball is swung in a horizontal circle of radius 1 m at a speed of 4 m/s. What is the tension in the string?

Accepted Answer

$$T = 32\ 	ext{N}$$

Question 13

A 50 kg person stands on a scale in a stationary elevator. What is the reading on the scale?

Accepted Answer

$$490\ 	ext{N}$$

Question 14

A 4 kg object is pulled by a force of 20 N horizontally. The coefficient of kinetic friction is $$\mu_k = 0.2. $$What is the acceleration of the object?

Accepted Answer

$$a = 3.0\ 	ext{m/s}^2$$

Question 15

A 1 kg object moves in a circle of radius 2 m with a period $$T = 4 s. $$What is its speed?

Accepted Answer

$$v = \frac{2 \pi r}{T} = \frac{4 \pi}{4} = \pi\ 	ext{m/s}$$

Question 16

A 7 kg box is pushed with a force of 50 N on a horizontal surface. The coefficient of kinetic friction is $$\mu_k = 0.3. $$What is the acceleration of the box?

Accepted Answer

$$a = 2.9\ 	ext{m/s}^2$$

Question 17

A 2 kg object is in equilibrium, suspended by two ropes at angles of $$30^\circ$$ and $$60^\circ to $$the horizontal. What is the sum of the vertical components of the tensions?

Accepted Answer

$$19.6\ 	ext{N}$$

Question 18

A 5 kg object is dropped from rest. What is its acceleration just after release?

Accepted Answer

$$a = 9.8\ 	ext{m/s}^2$$

Question 19

A 1 kg object is placed on a scale in a downward-accelerating elevator ($$a = 2\ 	ext{m/s}^2). $$What is the scale reading?

Accepted Answer

$$7.8\ 	ext{N}$$

Physics Study Guide: Forces, Newton's Laws, Equilibrium, Friction, and Circular Motion

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