Q: A 60.0 kg astronaut finds his weight on the Moon is 96.5 N. What is the acceleration due to gravity on the Moon?

$$g = \frac{96.5}{60.0} = 1.61\ \text{m/s}^2$$

Q: A student applies a horizontal 150 N force to a 45 kg desk causing it to accelerate at $$1.6\ \text{m/s}^2. $$What is the net force acting on the desk?

$$F_{net} = 45 \times 1.6 = 72\ \text{N}$$

Q: A 10 kg box is pushed with a force of 32 N to the left. The coefficient of kinetic friction is $$\mu_k = 0.17. $$What is the magnitude of the frictional force?

$$f_k = 0.17 \times 10 \times 9.8 = 16.7\ \text{N}$$

Q: What is the acceleration of a 1,600 kg rocket in deep space if it accelerates from rest to 40 m/s in 16.0 seconds?

$$a = \frac{40}{16} = 2.5\ \text{m/s}^2$$

Q: A 7 kg book sits on a table. What is the magnitude of the normal force acting on the book?

$$F_N = 7 \times 9.8 = 68.6\ \text{N}$$

Q: Brian, with a mass of 62 kg, steps in spilled milk with a coefficient of kinetic friction $$\mu_k = 0.040. $$What is the force of kinetic friction between Brian and the floor?

$$f_k = 0.040 \times 62 \times 9.8 = 24.3\ \text{N}$$

Question 1

According to Newton's First Law, what happens to an object when a net force is applied to it?

Accepted Answer

It will accelerate, changing its velocity.

Question 2

A 60.0 kg astronaut finds his weight on the Moon is 96.5 N. What is the acceleration due to gravity on the Moon?

Accepted Answer

$$g = \frac{96.5}{60.0} = 1.61\ 	ext{m/s}^2$$

Question 3

Which statement best describes the relationship between net force and acceleration according to Newton's Second Law?

Accepted Answer

Acceleration is directly proportional to net force.

Question 4

A student applies a horizontal 150 N force to a 45 kg desk causing it to accelerate at $$1.6\ 	ext{m/s}^2. $$What is the net force acting on the desk?

Accepted Answer

$$F_{net} = 45 	imes 1.6 = 72\ 	ext{N}$$

Question 5

A 10 kg box is pushed with a force of 32 N to the left. The coefficient of kinetic friction is $$\mu_k = 0.17. $$What is the magnitude of the frictional force?

Accepted Answer

$$f_k = 0.17 	imes 10 	imes 9.8 = 16.7\ 	ext{N}$$

Question 6

What is the acceleration of a 1,600 kg rocket in deep space if it accelerates from rest to 40 m/s in 16.0 seconds?

Accepted Answer

$$a = \frac{40}{16} = 2.5\ 	ext{m/s}^2$$

Question 7

Define static friction.

Accepted Answer

The friction force that prevents motion between two stationary surfaces.

Question 8

How does the coefficient of kinetic friction ($$\mu_k) $$compare to the coefficient of static friction ($$\mu_s$$)?

Accepted Answer

$$\mu_k is $$usually less than $$\mu_s.$$

Question 9

A 7 kg book sits on a table. What is the magnitude of the normal force acting on the book?

Accepted Answer

$$F_N = 7 	imes 9.8 = 68.6\ 	ext{N}$$

Question 10

Brian, with a mass of 62 kg, steps in spilled milk with a coefficient of kinetic friction $$\mu_k = 0.040. $$What is the force of kinetic friction between Brian and the floor?

Accepted Answer

$$f_k = 0.040 	imes 62 	imes 9.8 = 24.3\ 	ext{N}$$

Question 11

An object slides down an inclined plane. If the angle of the incline increases, what happens to the normal force?

Accepted Answer

The normal force decreases.

Question 12

A 2.5 kg object slides down an incline with $$\mu_k = 0.125$$ and normal force $$F_N = 23.5\ 	ext{N}. $$What is the frictional force?

Accepted Answer

$$f_k = 0.125 	imes 23.5 = 2.94\ 	ext{N}$$

Question 13

What condition is necessary for an object to be moving at terminal velocity?

Accepted Answer

The net force on the object is zero.

Question 14

A 40 kg object falls with a force of gravity of 400 N. What is its acceleration?

Accepted Answer

$$a = \frac{400}{40} = 10\ 	ext{m/s}^2$$

Question 15

A 75 kg skydiver has an acceleration of $$6.2\ 	ext{m/s}^2$$ downward. What is the net force acting on her?

Accepted Answer

$$F_{net} = 75 	imes 6.2 = 465\ 	ext{N}$$

Question 16

A 75 kg skydiver has a weight of 735 N. If her net force downward is 465 N, what is the air resistance acting on her?

Accepted Answer

$$F_{air} = 735 - 465 = 285\ 	ext{N}$$

Question 17

Which of the following best describes kinetic friction?

Accepted Answer

Friction that acts when surfaces are moving relative to each other.

Question 18

A cart with a total mass of 3 kg (including two 1 kg masses and the cart itself) is pulled with a net force of 6 N. What is its acceleration?

Accepted Answer

$$a = \frac{6}{3} = 2\ 	ext{m/s}^2$$

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