Q: A 2.0 kg box is released from rest at the top of a $$1.0\ \mathrm{m}$$ long ramp inclined at $$30^\circ. $$The coefficients of friction are $$\mu_k = 0.3$$ and $$\mu_s = 0.5. $$Will the box slide after being released?

Yes, because $$mg \sin \theta \u003e \mu_s mg \cos \theta$$

Q: A block of mass $$m = 5.8\ \mathrm{kg} is $$pulled up a frictionless incline of $$\theta = 25^\circ by a $$force $$F = 32\ \mathrm{N}$$ parallel to the incline. What is the acceleration of the block?

$$a = \dfrac{F - mg \sin \theta}{m} = 1.4\ \mathrm{m/s^2$}$$

Q: A 2.0 kg box is released from rest at the top of a $$1.0\ \mathrm{m}$$ long ramp inclined at $$30^\circ. $$The coefficients of friction are $$\mu_k = 0.3$$ and $$\mu_s = 0.5. $$What is the acceleration of the box once it starts moving?

$$a = g \sin \theta - \mu_k g \cos \theta = 2.35\ \mathrm{m/s^2$}$$

Question 1

A 30 kg child stands on a bathroom scale in an elevator that accelerates upward at $$0.5\ \mathrm{m/s^2$}. $$What does the scale read (in newtons)?

Accepted Answer

$$309.3\ \mathrm{N}$$

Question 2

Which of the following statements about equilibrium is correct?

Accepted Answer

An object is in equilibrium if $$\sum \vec{F} = 0$$, regardless of its velocity.

Question 3

A 5.0 kg object on a frictionless surface is acted on by a force of $$15\ \mathrm{N}$$ directed $$30^\circ$$ below the horizontal. What is the horizontal component of the acceleration?

Accepted Answer

$$a_x = \dfrac{15 \cos 30^\circ}{5.0} = 2.6\ \mathrm{m/s^2$}$$

Question 4

A 2.0 kg box is released from rest at the top of a $$1.0\ \mathrm{m}$$ long ramp inclined at $$30^\circ. $$The coefficients of friction are $$\mu_k = 0.3$$ and $$\mu_s = 0.5. $$Will the box slide after being released?

Accepted Answer

Yes, because $$mg \sin 	heta \u003e \mu_s mg \cos 	heta$$

Question 5

Which of the following best describes the normal force acting on an object at rest on a horizontal surface?

Accepted Answer

It is the force perpendicular to the surface that prevents the object from accelerating through the surface.

Question 6

A 150 N bird feeder is supported by two cables, one at $$60^\circ$$ and one at $$30^\circ to $$the horizontal. What is the tension in the cable at $$60^\circ$$?

Accepted Answer

$$T_1 = 130$$\ \mathrm{N}$$

Question 7

A block of mass $$m = 5.8\ \mathrm{kg} is $$pulled up a frictionless incline of $$	heta = 25^\circ by a $$force $$F = 32\ \mathrm{N}$$ parallel to the incline. What is the acceleration of the block?

Accepted Answer

$$a = \dfrac{F - mg \sin 	heta}{m} = 1.4\ \mathrm{m/s^2$}$$

Question 8

Which of the following statements about tension in a massless string is correct?

Accepted Answer

Tension is constant throughout the string.

Question 9

A 3 kg mass and a 10 kg mass are connected by a spring with $$k = 500\ \mathrm{N/m}$$ and compressed by $$0.05\ \mathrm{m}. $$What is the magnitude of the acceleration of the 3 kg mass when released?

Accepted Answer

$$a = 8.33\ \mathrm{m/s^2$}$$

Question 10

Which equation correctly gives the magnitude of the force of kinetic friction?

Accepted Answer

$$f_k = \mu_k n$$

Question 11

A spring is compressed by $$2.8\ \mathrm{cm}$$ and exerts a force of $$12\ \mathrm{N}. $$What is the spring constant $$k$$?

Accepted Answer

$$k = 429\ \mathrm{N/m}$$

Question 12

Which of the following is true about static friction?

Accepted Answer

Static friction can take any value up to $$\mu_s n to $$prevent motion.

Question 13

A 2.0 kg box is released from rest at the top of a $$1.0\ \mathrm{m}$$ long ramp inclined at $$30^\circ. $$The coefficients of friction are $$\mu_k = 0.3$$ and $$\mu_s = 0.5. $$What is the acceleration of the box once it starts moving?

Accepted Answer

$$a = g \sin 	heta - \mu_k g \cos 	heta = 2.35\ \mathrm{m/s^2$}$$

Question 14

Which of the following best describes the reading on a bathroom scale when you stand on it in an elevator accelerating downward?

Accepted Answer

The scale reads less than your true weight.

Question 15

Which of the following is NOT a correct step in applying Newton's Second Law to a problem?

Accepted Answer

Draw a free-body diagram for all objects at once.

Question 16

A block is at rest on a horizontal surface. Which of the following statements is true?

Accepted Answer

The normal force is always equal to the gravitational force.

Question 17

Which of the following best describes the direction of the spring force according to Hooke's Law?

Accepted Answer

It always opposes the direction of stretch or compression.

Question 18

In an Atwood machine, if both masses are equal and the pulley is frictionless, what is the acceleration of the system?

Accepted Answer

$$a = 0$$

Question 19

A block is being pulled across a horizontal surface at constant velocity. Which of the following is true?

Accepted Answer

The pulling force is equal to the kinetic friction force.

Chapter 5: Applying Newton's Laws – Forces and Equilibrium

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