Q: A 1.2 kg book lies on a table and is pressed down with a force of 15 N. What is the normal force $$n$$ exerted by the table?

$$n = 15 + (1.2 \times 9.8) N$$

Q: A box with weight 100 N is at rest. It is then pulled by a 30 N horizontal force. The coefficients of friction are $$\mu_s = 0.4$$ and $$\mu_k = 0.2. $$Does the box move?

No, because $$30 \u003c 0.4 \times 100$$

Question 1

An orangutan weighing 500 N hangs motionless from a vertical rope as shown in the diagram. What is the tension $$T in $$the rope?

Accepted Answer

$$T = 500 N$$

Question 2

A rod is free to slide on a frictionless sheet of ice. One end of the rod is lifted by a string. If the rod is at rest, which orientation of the string ensures static equilibrium?

Accepted Answer

The string is vertical

Question 3

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 $$f = 320 N. $$What is the tension $$T in $$the rope?

Accepted Answer

$$T = \frac{320}{\cos 20^\circ} N$$

Question 4

A 1.2 kg book lies on a table and is pressed down with a force of 15 N. What is the normal force $$n$$ exerted by the table?

Accepted Answer

$$n = 15 + (1.2 	imes 9.8) N$$

Question 5

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

Accepted Answer

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

Question 6

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

Accepted Answer

$$\u003e 490 N$$

Question 7

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

Accepted Answer

$$n \u003c mg$$

Question 8

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 $$f_s$$?

Accepted Answer

$$f_s = T$$

Question 9

A box with weight 100 N is at rest. It is then pulled by a 30 N horizontal force. The coefficients of friction are $$\mu_s = 0.4$$ and $$\mu_k = 0.2. $$Does the box move?

Accepted Answer

No, because $$30 \u003c 0.4 	imes 100$$

Question 10

A 75 kg skydiver and a 0.020 kg mouse fall from a plane. At terminal speed, what is true about the forces acting on each?

Accepted Answer

Drag force equals gravity

Question 11

Two blocks, A (5 kg) and B (10 kg), are pushed together on a frictionless surface by a 3 N force. What force does block A exert on block B?

Accepted Answer

$$2 N$$

Question 12

A 5 kg block is connected by a massless rope over a massless, frictionless pulley to another 5 kg block. What is the tension in the rope if the system is at rest?

Accepted Answer

$$49 N$$

Question 13

A block of mass $$m is $$accelerated across a frictionless table by a falling mass $$m. $$The string is massless, and the pulley is frictionless. What is the tension $$T in $$the string compared to $$mg$$?

Accepted Answer

$$T \u003c mg$$

Question 14

A 200 kg stage set is held by a rope over a pulley. A 100 kg stagehand holds the other end. When the rope is released, what is the acceleration $$a of $$the stage set?

Accepted Answer

$$a = \frac{(200 - 100)g}{200 + 100}$$

Question 15

A 50-kg student stands on a scale in an elevator. The elevator cable breaks and the elevator falls freely. What does the scale read?

Accepted Answer

$$0 N$$

Question 16

A box is being pulled to the right over a rough surface. The tension $$T in $$the rope is greater than the kinetic friction $$f_k. $$Suddenly the rope breaks. What happens to the box?

Accepted Answer

It slows steadily until it stops

Question 17

A 46 g golf ball is putted at 3.0 m/s. Friction exerts a 0.020 N retarding force. What is the acceleration $$a of $$the ball?

Accepted Answer

$$a = -0.020 / 0.046 m/s$^2$$

Question 18

A block is at rest on an incline. Which force always points perpendicular to the surface?

Accepted Answer

Normal force

Question 19

A box is being pushed across a floor at constant speed. What is true about the pushing force $$F$$ and the kinetic friction $$f_k$$?

Accepted Answer

$$F = f_k$$

Question 20

A 100-kg block is hanging from a rope and is moving upward at a steady speed. What is the tension $$T in $$the rope?

Accepted Answer

$$T = 100 	imes 9.8 N$$

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

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