Q: A penguin jumps out of the water and lands on an ice floe, as shown in the image. Which of the following best describes the net force acting on the penguin at the highest point of its trajectory (neglecting air resistance)?

The net force is equal to the gravitational force, $$F_{\text{net}} = mg$$, directed downward.

Q: A 110-kg basketball player hangs motionless from a rim, which deflects downward by 0.15 m. If the rim behaves like a spring, what is the force constant $$k of $$the rim? (Take $$g = 9.8\ \text{m/s}^2)$$

$$k = \frac{mg}{x} = \frac{110 \times 9.8}{0.15}$$

Q: A car rounds a frictionless banked curve of radius $$r at $$speed $$v. $$What is the correct expression for the banking angle $$\theta$$ required for no friction to be needed?

$$\tan\theta = \frac{v^2$}{rg}$$

Q: A coin rests on a book cover. As you slowly tilt the book, the coin begins to slide at angle $$\theta_{\text{max}}. $$What is the coefficient of static friction $$\mu_s$$ between the coin and the cover?

$$\mu_s = \tan\theta_{\text{max}}$$

Q: A box of mass $$m is $$pulled across a horizontal surface with a force $$F at an $$angle $$\theta$$ above the horizontal. If the coefficient of kinetic friction is $$\mu_k$$, what is the expression for the acceleration of the box?

$$a = \frac{F\cos\theta - \mu_k mg}{m}$$

Question 1

A penguin jumps out of the water and lands on an ice floe, as shown in the image. Which of the following best describes the net force acting on the penguin at the highest point of its trajectory (neglecting air resistance)?

Accepted Answer

The net force is equal to the gravitational force, $$F_{	ext{net}} = mg$$, directed downward.

Question 2

A box rests on a table. Which of the following forces act on the box? (Refer to the free-body diagram images.)

Accepted Answer

Both the normal force and the gravitational force.

Question 3

A 5-kg box and a 10-kg box are pushed with the same force on a frictionless surface. According to Newton's second law, what is the ratio of their accelerations?

Accepted Answer

$$a_{5}/a_{10} = 2$$

Question 4

A person stands on a scale in an elevator accelerating upward with acceleration $$a. If $$the person's mass is $$m$$, what does the scale read?

Accepted Answer

$$N = m(g + a)$$

Question 5

A book sits at rest on a table. Which of the following forces should NOT appear on the free-body diagram for the book?

Accepted Answer

The force of the book on the table.

Question 6

A spring is compressed by a distance $$x$$ from its equilibrium position. According to Hooke's Law, what is the force exerted by the spring?

Accepted Answer

$$F = -kx$$

Question 7

A 110-kg basketball player hangs motionless from a rim, which deflects downward by 0.15 m. If the rim behaves like a spring, what is the force constant $$k of $$the rim? (Take $$g = 9.8\ 	ext{m/s}^2)$$

Accepted Answer

$$k = \frac{mg}{x} = \frac{110 	imes 9.8}{0.15}$$

Question 8

A car rounds a frictionless banked curve of radius $$r at $$speed $$v. $$What is the correct expression for the banking angle $$	heta$$ required for no friction to be needed?

Accepted Answer

$$	an	heta = \frac{v^2$}{rg}$$

Question 9

A coin rests on a book cover. As you slowly tilt the book, the coin begins to slide at angle $$	heta_{	ext{max}}. $$What is the coefficient of static friction $$\mu_s$$ between the coin and the cover?

Accepted Answer

$$\mu_s = 	an	heta_{	ext{max}}$$

Question 10

A 20-ton truck collides with a 1500-lb car. According to Newton's third law, during the collision:

Accepted Answer

The forces on both vehicles are equal in magnitude and opposite in direction.

Question 11

A mass $$m is $$suspended from a spring and released. While accelerating downward, the magnitude of the spring force is:

Accepted Answer

Smaller than the weight of the mass.

Question 12

A box of mass $$m is $$pulled across a horizontal surface with a force $$F at an $$angle $$	heta$$ above the horizontal. If the coefficient of kinetic friction is $$\mu_k$$, what is the expression for the acceleration of the box?

Accepted Answer

$$a = \frac{F\cos	heta - \mu_k mg}{m}$$

Question 13

A tetherball of mass $$m$$ swings in a horizontal circle of radius $$r at $$speed $$v$$, with the rope making an angle $$	heta$$ with the vertical. What is the tension $$T in $$the rope?

Accepted Answer

$$T = \frac{mg}{\cos	heta}$$

Question 14

Two blocks are connected by a light string and pulled across a frictionless surface. If a force $$F is $$applied to the second block, which statement is true about the tension in the string?

Accepted Answer

The tension is less than $$F$$ but not zero.

Question 15

A brick is resting on a rough incline. The friction force acting on the brick, along the incline, is:

Accepted Answer

Less than the weight of the brick.

Question 16

A roller coaster car of mass $$m$$ goes around a vertical loop of radius $$r. $$What is the minimum speed $$v_{	ext{min}} at $$the top of the loop to stay on the track?

Accepted Answer

$$v_{	ext{min}} = \sqrt{gr}$$

Question 17

If you move from Earth to the Moon, which of the following changes?

Accepted Answer

Your weight changes, but your mass does not.

Question 18

A person in a freely falling elevator feels weightless because:

Accepted Answer

The normal force is zero.

Question 19

Which of the following is NOT a fundamental force of nature?

Accepted Answer

Frictional force

Newton's Laws of Motion and Applications: Forces, Friction, and Circular Motion

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