Q: A 1500 kg car is towed by a rope at a 20° angle to the horizontal. A friction force of 320 N opposes the motion. If the car accelerates from rest to 12 m/s in 10 s, what is the tension in the rope?

$$T = \frac{320 + (1500 \times 1.2)}{\cos 20^\circ} = 2020\ \mathrm{N}$$

Q: A 100 N box is at rest on a horizontal surface. The coefficient of static friction is $$\mu_s = 0.4. If a 30 N $$horizontal force is applied, does the box move?

No, because $$f_{s,\text{max}} = \mu_s n = 40\ \mathrm{N} \u003e 30\ \mathrm{N}$$

Q: A 20 kg curling stone is pushed to a speed of 3.0 m/s over 2.0 s. Ignoring friction, what is the force applied?

$$F = m a = m \frac{\Delta v}{\Delta t} = 20 \times \frac{3.0}{2.0} = 30\ \mathrm{N}$$

Q: A curling stone (20 kg) is launched at 3 m/s and travels 40 m before stopping. What is the magnitude of the friction force?

$$f = \frac{1}{2} m v^2$ / d = \frac{1}{2} \times 20 \times 9 / 40 = 2.25\ \mathrm{N}$$

Q: A 5.0 kg block A is pushed with a 3.0 N force against a 10 kg block B on a frictionless surface. What force does block A exert on block B?

$$F = \frac{10}{15} \times 3.0 = 2.0\ \mathrm{N}$$

Question 1

A 1500 kg car is being towed at a steady speed by a rope held at a 20° angle from the horizontal. A friction force of 320 N opposes the car’s motion. What is the tension in the rope?

Accepted Answer

$$T = \frac{320}{\cos 20^\circ} = 340\ \mathrm{N}$$

Question 2

A 1500 kg car is towed by a rope at a 20° angle to the horizontal. A friction force of 320 N opposes the motion. If the car accelerates from rest to 12 m/s in 10 s, what is the tension in the rope?

Accepted Answer

$$T = \frac{320 + (1500 	imes 1.2)}{\cos 20^\circ} = 2020\ \mathrm{N}$$

Question 3

Which of the following best describes the difference between mass and weight?

Accepted Answer

Mass is the amount of matter in an object and is constant everywhere; weight is the gravitational force on an object and varies with location.

Question 4

A person stands on a scale in an elevator accelerating upward with acceleration $$a. $$What does the scale read?

Accepted Answer

$$n = m(g + a)$$

Question 5

A box is being pulled to the right at steady speed by a rope that angles upward. In this situation, how does the normal force $$n$$ compare to the weight $$mg$$?

Accepted Answer

$$n \u003c mg$$

Question 6

A 100 N box is at rest on a horizontal surface. The coefficient of static friction is $$\mu_s = 0.4. If a 30 N $$horizontal force is applied, does the box move?

Accepted Answer

No, because $$f_{s,	ext{max}} = \mu_s n = 40\ \mathrm{N} \u003e 30\ \mathrm{N}$$

Question 7

A 20 kg curling stone is pushed to a speed of 3.0 m/s over 2.0 s. Ignoring friction, what is the force applied?

Accepted Answer

$$F = m a = m \frac{\Delta v}{\Delta t} = 20 	imes \frac{3.0}{2.0} = 30\ \mathrm{N}$$

Question 8

A curling stone (20 kg) is launched at 3 m/s and travels 40 m before stopping. What is the magnitude of the friction force?

Accepted Answer

$$f = \frac{1}{2} m v^2$ / d = \frac{1}{2} 	imes 20 	imes 9 / 40 = 2.25\ \mathrm{N}$$

Question 9

If the mass of the curling stone is doubled but the launch speed is the same, what happens to the distance it travels before stopping (assuming the same friction coefficient)?

Accepted Answer

It travels the same distance.

Question 10

Which action by a curling sweeper will make the stone travel farther?

Accepted Answer

Decreasing the coefficient of friction between the stone and the ice.

Question 11

A 5.0 kg block A is pushed with a 3.0 N force against a 10 kg block B on a frictionless surface. What force does block A exert on block B?

Accepted Answer

$$F = \frac{10}{15} 	imes 3.0 = 2.0\ \mathrm{N}$$

Question 12

Two boxes, A and B, are connected by a rope and pulled to the right on a frictionless surface. Box A has a larger mass than Box B. How do the two tension forces compare?

Accepted Answer

$$T_1$$ \u003e $$T_2$$

Question 13

A massless string passes over a massless, frictionless pulley connecting two 5 kg masses. What does the scale in the middle read?

Accepted Answer

10 kg

Question 14

Which of the following best describes the drag force $$\vec{D}$$ acting on an object moving through a fluid?

Accepted Answer

It acts opposite to the velocity and increases with speed.

Question 15

For a sphere of radius $$r$$ moving through air, what is the cross-sectional area $$A$$ used in the drag force equation?

Accepted Answer

$$A = \pi r^2$

Question 16

A falling object reaches terminal speed when:

Accepted Answer

The drag force equals the weight force.

Question 17

Which of the following is true about rolling friction compared to kinetic friction?

Accepted Answer

Rolling friction is generally much smaller than kinetic friction.

Chapter 5: Applying Newton’s Laws – Physics with Calculus Study Guide

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