Question 1

A hockey puck slides across a perfectly frictionless ice surface after being hit. According to Newton's first law, what will happen to the puck if no other forces act on it?

Accepted Answer

It will continue moving in a straight line at constant speed.

Question 2

A 10 kg box rests on a horizontal floor. The coefficient of static friction is 0.40. What is the maximum force of static friction that can act on the box before it starts to move? Use $$g = 9.8\ \mathrm{m/s^2$}.$$

Accepted Answer

$$39.2\ \mathrm{N}$$

Question 3

A car is parked on a hill. Which forces must be included in its free-body diagram?

Accepted Answer

Weight, normal force, and static friction

Question 4

A 1.0 kg block is pulled with a constant force and accelerates at $$3.0\ \mathrm{m/s^2$}. A $$second block, with unknown mass, is pulled with the same force and accelerates at $$5.0\ \mathrm{m/s^2$}. $$What is the mass of the second block?

Accepted Answer

$$0.60\ \mathrm{kg}$$

Question 5

A ball is thrown straight up. Just after it leaves the thrower's hand (neglecting air resistance), what force(s) act on it?

Accepted Answer

Only gravity

Question 6

A 40-car train travels at constant speed on a straight track, while a skier speeds up as she skis downhill. On which is the net force greater?

Accepted Answer

The skier

Question 7

A box is pushed across a table at a steady speed. Which statement is true about the forces acting on the box?

Accepted Answer

The pushing force is equal to the friction force.

Question 8

A steel beam hangs from a cable as a crane lifts the beam upward at constant speed. What forces act on the beam?

Accepted Answer

Gravity and tension in the cable

Question 9

A mosquito collides head-on with a truck. According to Newton’s third law, which statement is true during the collision?

Accepted Answer

The mosquito exerts the same force on the truck as the truck exerts on the mosquito.

Question 10

A 51,000 kg airplane accelerates from rest to $$70\ \mathrm{m/s}$$ over a distance of $$940\ \mathrm{m} on a $$runway. What is the total thrust force produced by the engines? (Assume constant acceleration.)

Accepted Answer

$$133,000\ \mathrm{N}$$

Question 11

A bungee jumper is nearing the bottom of her fall. What forces are acting on her at that instant?

Accepted Answer

Tension from the cord and weight

Question 12

A block is being pulled to the right with a constant, steady force. What does the acceleration vs. time graph look like?

Accepted Answer

A horizontal line above zero (constant acceleration)

Question 13

A 10 kg box is held against a rough vertical wall by pressing horizontally. What force prevents the box from sliding down?

Accepted Answer

Static friction

Question 14

A ball rolls down an incline and leaves a horizontal ramp. Ignoring air resistance, what force(s) act on the ball as it moves through the air just after leaving the ramp?

Accepted Answer

The weight of the ball acting vertically down

Question 15

A car is towed to the right at constant speed. What can you say about the net force acting on the car?

Accepted Answer

The net force is zero

Question 16

A constant force causes an object to accelerate at $$4\ \mathrm{m/s^2$}. $$What is the acceleration if the same force is applied to an object with twice the mass?

Accepted Answer

$$2\ \mathrm{m/s^2$}$$

Question 17

A person stands on a scale in an elevator that is moving upward and slowing down. How does the reading on the scale compare to the person's true weight?

Accepted Answer

The scale reads less than the true weight

Question 18

A block is being pulled across a rough surface at constant speed. Which of the following statements is true?

Accepted Answer

The applied force equals the kinetic friction force

Question 19

A rocket launches vertically upward. What is the direction of the thrust force acting on the rocket?

Accepted Answer

Upward, opposite to the direction of the expelled gases

Chapter 4: Forces and Newton’s Laws of Motion – Study Guide

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