Q: An otter is sitting on an 85 cm long incline and begins sliding toward the bottom from rest. If it takes the otter 2.0 s to reach the bottom, what is the net force acting on the otter if its mass is 5.0 kg? (Assume constant acceleration and no friction.)

$$F = m a = 5.0 \times \frac{2 \times 0.85}{(2.0)^2$} = 2.125\ \mathrm{N}$$

Question 1

Which of the following best describes Newton's First Law of Motion?

Accepted Answer

An object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.

Question 2

A 10 kg box is at rest on a frictionless surface. According to Newton's First Law, what will happen if no net force acts on the box?

Accepted Answer

The box will remain at rest.

Question 3

A truck carrying a large stone suddenly stops, but the stone slides forward and crashes into the cab. This scenario best illustrates which concept?

Accepted Answer

Inertia

Question 4

Which of the following is an example of a contact force?

Accepted Answer

Friction

Question 5

A climber is descending a cliff and is held by a rope. Which force diagram best represents the forces acting on the climber?

Accepted Answer

An upward force from the rope and a downward force due to gravity.

Question 6

If a 77 N force is pulling an object straight down and a 35 N force is pulling it to the right, what is the magnitude of the net force acting on the object?

Accepted Answer

$$\sqrt{77^2$ + 35^2$} = 84.3\ \mathrm{N}$$

Question 7

Which of the following statements about Newton's Third Law is correct?

Accepted Answer

For every action, there is an equal and opposite reaction.

Question 8

A rocket engine expels exhaust gases backward. According to Newton's Third Law, what happens to the rocket?

Accepted Answer

The rocket is pushed forward with an equal and opposite force.

Question 9

A quarterback is being sacked and falls to the ground. Which forces are acting on him during the fall?

Accepted Answer

Gravity pulling down and air resistance pushing up.

Question 10

An otter is sitting on an 85 cm long incline and begins sliding toward the bottom from rest. If it takes the otter 2.0 s to reach the bottom, what is the net force acting on the otter if its mass is 5.0 kg? (Assume constant acceleration and no friction.)

Accepted Answer

$$F = m a = 5.0 	imes \frac{2 	imes 0.85}{(2.0)^2$} = 2.125\ \mathrm{N}$$

Question 11

Which of the following best defines inertia?

Accepted Answer

The tendency of an object to resist a change in its motion.

Question 12

A net force of 20 N is applied to a 4 kg object. What is the acceleration of the object?

Accepted Answer

$$a = \frac{F}{m} = \frac{20}{4} = 5\ \mathrm{m/s^2$}$$

Question 13

Which of the following is NOT a non-contact force?

Accepted Answer

Friction

Question 14

A soccer ball is kicked and moves in a straight line at constant speed. What can you conclude about the net force acting on the ball?

Accepted Answer

The net force is zero.

Question 15

A 2 kg object is acted on by two forces: 6 N to the right and 8 N to the left. What is the acceleration of the object?

Accepted Answer

$$a = \frac{6 - 8}{2} = -1\ \mathrm{m/s^2$}$$

Question 16

Which of the following real-life scenarios best demonstrates Newton's Third Law?

Accepted Answer

A swimmer pushes water backward, and the water pushes the swimmer forward.

Question 17

If the net force acting on an object is zero, which of the following must be true?

Accepted Answer

The object is either at rest or moving at constant velocity.

Question 18

A 3 kg object is moving at 4 m/s. If a net force of 9 N acts in the direction of motion for 2 seconds, what will be the final velocity?

Accepted Answer

$$v_f = v_i + a t = 4 + \frac{9}{3} 	imes 2 = 10\ \mathrm{m/s}$$

Question 19

Which of the following statements is true regarding net force?

Accepted Answer

Net force is the vector sum of all forces acting on an object.

Forces and Motion: Newton's Laws and Applications

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