Q: A 5-kg box is pushed across a rough floor with a constant force of 20 N. If the frictional force opposing the motion is 8 N, what is the acceleration of the box?

$$a = \frac{20 - 8}{5} = 2.4\ \text{m/s}^2$$

Q: A 10-kg object is in free fall near Earth's surface. What is the net force acting on it, ignoring air resistance?

$$F_{\text{net}} = 98\ \text{N}$$

Q: A 2-kg object is acted upon by a net force of 12 N. What is its acceleration?

$$a = \frac{12}{2} = 6\ \text{m/s}^2$$

Q: A 1000-kg car experiences a net force of 2000 N. What is its acceleration?

$$a = \frac{2000}{1000} = 2\ \text{m/s}^2$$

Q: A 20,000-kg jet accelerates at $$1.5\ \text{m/s}^2. $$What thrust is required?

$$F = 20,000 \times 1.5 = 30,000\ \text{N}$$

Question 1

A 5-kg box is pushed across a rough floor with a constant force of 20 N. If the frictional force opposing the motion is 8 N, what is the acceleration of the box?

Accepted Answer

$$a = \frac{20 - 8}{5} = 2.4\ 	ext{m/s}^2$$

Question 2

Which of the following statements about friction is TRUE?

Accepted Answer

Friction does not depend on the contact area between surfaces.

Question 3

A 1-kg object weighs approximately 9.8 N on Earth. What would its weight be on the Moon, where gravity is about $$\frac{1}{6}$$ that of Earth?

Accepted Answer

$$1.6\ 	ext{N}$$

Question 4

A skydiver reaches terminal velocity when:

Accepted Answer

The air resistance equals the force of gravity and acceleration becomes zero.

Question 5

If you double the net force acting on an object while keeping its mass constant, what happens to its acceleration?

Accepted Answer

The acceleration doubles.

Question 6

A 10-kg object is in free fall near Earth's surface. What is the net force acting on it, ignoring air resistance?

Accepted Answer

$$F_{	ext{net}} = 98\ 	ext{N}$$

Question 7

Which scenario best demonstrates the concept of inertia?

Accepted Answer

A person jerks a string attached to a hanging ball, causing the bottom string to break.

Question 8

A 2-kg object is acted upon by a net force of 12 N. What is its acceleration?

Accepted Answer

$$a = \frac{12}{2} = 6\ 	ext{m/s}^2$$

Question 9

Which of the following is NOT a property of solid friction?

Accepted Answer

It increases with the mass of the object.

Question 10

A 1000-kg car experiences a net force of 2000 N. What is its acceleration?

Accepted Answer

$$a = \frac{2000}{1000} = 2\ 	ext{m/s}^2$$

Question 11

Which of the following best explains why a heavy boulder and a light feather fall at the same rate in a vacuum?

Accepted Answer

The ratio of gravitational force to mass is constant for all objects.

Question 12

A 20,000-kg jet accelerates at $$1.5\ 	ext{m/s}^2. $$What thrust is required?

Accepted Answer

$$F = 20,000 	imes 1.5 = 30,000\ 	ext{N}$$

Question 13

Which of the following statements about fluid friction is correct?

Accepted Answer

Fluid friction increases with speed.

Question 14

A 4-kg block is pushed with a force of 12 N against 6 N of friction. What is its acceleration?

Accepted Answer

$$a = \frac{12 - 6}{4} = 1.5\ 	ext{m/s}^2$$

Question 15

If a jet flies at a constant velocity, what can be said about the net force acting on it?

Accepted Answer

The net force is zero.

Question 16

A heavier parachutist and a lighter parachutist use identical parachutes. Who will reach the ground first and why?

Accepted Answer

The heavier parachutist, because they must fall faster to reach terminal velocity.

Question 17

Which formula correctly expresses Newton’s Second Law?

Accepted Answer

$$F_{	ext{net}} = m \cdot a$$

Question 18

What is the acceleration of a 1-kg object in free fall near Earth’s surface?

Accepted Answer

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

Question 19

Which of the following best describes the effect of friction when pushing an object across a rough surface compared to a smooth surface?

Accepted Answer

The acceleration is less on the rough surface due to increased friction.

Forces, Friction, Mass, Weight, and Newton’s Second Law (Chapter 4)

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