Q: A 20.0 kg box $$A$$ and a 5.0 kg box $$B$$ are in contact on a frictionless surface. A force of 250 N is applied to box $$A. $$What is the force that $$A$$ exerts on $$B$$?

$$F = 250 \times \frac{5.0}{25.0} = 50\ \mathrm{N}$$

Question 1

Which of the following statements best describes the normal force acting on an object resting on a flat surface?

Accepted Answer

It acts perpendicular to the surface and supports the object's weight.

Question 2

A 10-N force is applied at an angle of $$30^\circ$$ above the horizontal to a box on a frictionless surface. What is the vertical component of this force?

Accepted Answer

$$10 \sin 30^\circ = 5.0\ \mathrm{N}$$

Question 3

Which of the following is NOT a property of a force?

Accepted Answer

A force can exist without any interaction.

Question 4

A hockey puck on a frictionless surface is acted on by a single horizontal force $$\vec{F}_1. $$What happens to the puck?

Accepted Answer

It accelerates in the direction of $$\vec{F}_1.$$

Question 5

Three wrestlers pull on a belt with forces $$F_1 = 50$$\ \mathrm{N}$$ (along +x$), F_2$ = 120\ \mathrm{N} ($$along $$-y$$), and $$F_3 = 250$$\ \mathrm{N}$$ at 53$$^\circ$$ above the -x$ axis. What is the x$-component of the net force?

Accepted Answer

$$50 - 250 \cos 53^\circ$$

Question 6

According to Newton's First Law, what condition must be met for an object to be in equilibrium?

Accepted Answer

The net external force on the object must be zero: $$\sum \vec{F} = 0.$$

Question 7

A 12.0 kg chair is pushed with a force of $$F = 40.0\ \mathrm{N} at$$ $$37.0^\circ$$ below the horizontal on a frictionless floor. What is the normal force $$n$$ exerted by the floor?

Accepted Answer

$$n = mg + F \sin 37.0^\circ$$

Question 8

Which of the following best describes the direction of the net force on an object in uniform circular motion?

Accepted Answer

Toward the center of the circle.

Question 9

A box of mass $$m is $$suspended by a rope and is at rest. Which equation correctly relates the tension $$T in $$the rope to the weight $$w of $$the box?

Accepted Answer

$$T = mg$$

Question 10

A 20.0 kg box $$A$$ and a 5.0 kg box $$B$$ are in contact on a frictionless surface. A force of 250 N is applied to box $$A. $$What is the force that $$A$$ exerts on $$B$$?

Accepted Answer

$$F = 250 	imes \frac{5.0}{25.0} = 50\ \mathrm{N}$$

Question 11

Which of the following is an example of Newton's Third Law in action?

Accepted Answer

A swimmer pushes water backward and moves forward.

Question 12

A runner pushes backward on the starting block with a force $$\vec{F}. $$According to Newton's Third Law, what is the reaction force?

Accepted Answer

The block pushes forward on the runner with force $$-\vec{F}.$$

Question 13

A box is sliding across a rough surface. Which force is responsible for slowing it down?

Accepted Answer

Friction force

Question 14

If the net external force on an object is doubled, what happens to its acceleration?

Accepted Answer

It is doubled.

Question 15

A 5 kg object is acted on by a net force of 20 N. What is its acceleration?

Accepted Answer

$$a = 4\ \mathrm{m/s^2$}$$

Question 16

Which of the following is true about the weight of an object?

Accepted Answer

It depends on the gravitational acceleration $$g at $$the object's location.

Question 17

A bus accelerates forward and you are standing inside. Why do you feel as if you are moving backward?

Accepted Answer

Because your body tends to remain at rest due to inertia.

Question 18

Which of the following is the correct vector equation for Newton's Second Law?

Accepted Answer

$$\sum \vec{F} = m \vec{a}$$

Newton’s Laws of Motion: Forces and Applications

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