Q: A 100 N box is at rest on a horizontal surface. The coefficient of static friction is $$\mu_s = 0.4. $$What is the maximum static friction force?

$$f_{s,\text{max}} = 0.4 \times 100 = 40 N$$

Q: A 75 kg skydiver reaches terminal speed when the drag force equals the weight. Which equation gives the terminal speed $$v_{\text{term}}$$ for high Reynolds number drag?

$$v_{\text{term}} = \sqrt{\frac{2mg}{C_D \rho A}}$$

Q: A pollen grain of radius $$r$$ falls at terminal speed $$v_{\text{term}} in $$air (low Reynolds number). What is the drag force acting on it?

$$F_D = 6 \pi \eta r v_{\text{term}}$$

Q: A 200 kg stage set is connected by a rope over a pulley to a 100 kg stagehand. When the rope is released, what is the acceleration of the stagehand?

$$a = \frac{(m_{\text{set}} - m_{\text{man}})g}{m_{\text{set}} + m_{\text{man}}}$$

Question 1

A 500 N orangutan hangs motionless from a vertical rope. What is the tension in the rope?

Accepted Answer

$$T = 500 N$$

Question 2

A car with mass $$m = 1500 kg is $$towed at a steady speed by a rope at a $$20^\circ$$ angle above the horizontal. The friction force is $$320 N. $$What is the horizontal component of the tension in the rope?

Accepted Answer

$$T_x = 320 N$$

Question 3

A 1.2 kg book is pressed down on a table with an additional force of 15 N. What is the normal force exerted by the table?

Accepted Answer

$$n = mg + 15 N$$

Question 4

A skier slides down a frictionless $$27^\circ$$ slope. What is the skier’s acceleration?

Accepted Answer

$$a = g \sin 27^\circ$$

Question 5

A 50-kg student stands on a scale in an elevator accelerating upward. What does the scale read?

Accepted Answer

$$n \u003e mg$$

Question 6

A box is pulled to the right at steady speed by a rope that angles upward. How does the normal force compare to the box’s weight?

Accepted Answer

$$n \u003c mg$$

Question 7

A 100 N box is at rest on a horizontal surface. The coefficient of static friction is $$\mu_s = 0.4. $$What is the maximum static friction force?

Accepted Answer

$$f_{s,	ext{max}} = 0.4 	imes 100 = 40 N$$

Question 8

A 32 kg sofa is pushed at a steady speed across the floor with $$\mu_k = 0.08. $$What force does Carol apply?

Accepted Answer

$$F = \mu_k mg$$

Question 9

A 75 kg skydiver reaches terminal speed when the drag force equals the weight. Which equation gives the terminal speed $$v_{	ext{term}}$$ for high Reynolds number drag?

Accepted Answer

$$v_{	ext{term}} = \sqrt{\frac{2mg}{C_D ho A}}$$

Question 10

A pollen grain of radius $$r$$ falls at terminal speed $$v_{	ext{term}} in $$air (low Reynolds number). What is the drag force acting on it?

Accepted Answer

$$F_D = 6 \pi \eta r v_{	ext{term}}$$

Question 11

Two blocks, A (5 kg) and B (10 kg), are pushed together with a force of 3 N on a frictionless surface. What is the force that block A exerts on block B?

Accepted Answer

$$F_{A 	ext{ on } B} = 2 N$$

Question 12

A 70 kg man stands on a scale in an elevator moving downward and slowing to a stop. The scale reads 750 N. What is the direction of the elevator’s acceleration?

Accepted Answer

Upward

Question 13

A box is being pulled to the right over a rough surface. The rope breaks. What happens to the box?

Accepted Answer

It slows steadily until it stops.

Question 14

A 50-kg student stands on a scale in a falling elevator (cable breaks). What does the scale read?

Accepted Answer

$$0 N$$

Question 15

A box on a rough surface is pulled by a horizontal rope with tension $$T. $$The box is not moving. What is the static friction force?

Accepted Answer

$$f_s = T$$

Question 16

A 200 kg stage set is connected by a rope over a pulley to a 100 kg stagehand. When the rope is released, what is the acceleration of the stagehand?

Accepted Answer

$$a = \frac{(m_{	ext{set}} - m_{	ext{man}})g}{m_{	ext{set}} + m_{	ext{man}}}$$

Question 17

Which of the following is true about the tension in a massless rope passing over a massless, frictionless pulley?

Accepted Answer

The tension is the same at all points in the rope.

Question 18

A car accelerates from rest to $$12 m/s in$$ $$10 s. $$What is its acceleration?

Accepted Answer

$$a = 1.2 m/s$^2$$

Question 19

Which of the following best describes the difference between mass and weight?

Accepted Answer

Mass is the measure of inertia; weight is the gravitational force on an object.

Applying Newton’s Laws: Equilibrium, Dynamics, Forces, and Interactions

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