Q: A 5 kg object is pulled across a horizontal surface with a constant velocity by a force of 20 N. What is the coefficient of kinetic friction $$\mu_k$$ between the object and the surface?

$$\mu_k = \frac{20}{5 \times 9.8}$$

Q: A 70 kg astronaut weighs less on the Moon than on Earth. If the acceleration due to gravity on the Moon is $$1.6\,\mathrm{m/s^2$}$$, what is the astronaut's weight on the Moon?

$$70 \times 1.6 = 112\,\mathrm{N}$$

Q: A 10 kg box is at rest on a horizontal surface. What is the normal force acting on the box?

$$F_N = mg = 10 \times 9.8 = 98\,\mathrm{N}$$

Question 1

A 2 kg object is suspended from a spring and remains at rest. Which of the following best describes the forces acting on the object according to Newton's First Law?

Accepted Answer

The net force on the object is zero because the upward spring force balances the downward gravitational force.

Question 2

A car of mass $$m$$ rounds a flat curve of radius $$r at $$constant speed $$v. $$What is the minimum coefficient of static friction $$\mu_s$$ required to prevent the car from sliding?

Accepted Answer

$$\mu_s = \frac{v^2$}{rg}$$

Question 3

Which of the following best describes the apparent weight of a person in an elevator accelerating upward with acceleration $$a$$?

Accepted Answer

Apparent weight is $$m(g + a)$$, where $$m is $$the person's mass.

Question 4

A satellite orbits Earth at a constant speed in a circular orbit of radius $$r. $$Which equation correctly relates the gravitational force to the required centripetal force?

Accepted Answer

$$\frac{GMm}{r^2$} = \frac{mv^2$}{r}$$

Question 5

A block slides down a frictionless incline. Which of the following statements is true about the forces acting on the block?

Accepted Answer

The normal force acts perpendicular to the surface, and gravity acts vertically downward.

Question 6

If the period $$T of a $$planet's orbit around the Sun is known, which equation allows you to determine the radius $$r of $$its orbit?

Accepted Answer

$$T^2$$ = \left( \frac{4\$$pi^2$$}{GM} \right) $$r^3$$

Question 7

A 5 kg object is pulled across a horizontal surface with a constant velocity by a force of 20 N. What is the coefficient of kinetic friction $$\mu_k$$ between the object and the surface?

Accepted Answer

$$\mu_k = \frac{20}{5 	imes 9.8}$$

Question 8

Which of the following best describes the direction of the tension force in a rope connecting two objects?

Accepted Answer

Tension always pulls away from the objects along the direction of the rope.

Question 9

A ball of mass $$m is $$whirled in a horizontal circle of radius $$r at $$constant speed $$v. $$What is the expression for the centripetal acceleration?

Accepted Answer

$$a_c = \frac{v^2$}{r}$$

Question 10

A 70 kg astronaut weighs less on the Moon than on Earth. If the acceleration due to gravity on the Moon is $$1.6\,\mathrm{m/s^2$}$$, what is the astronaut's weight on the Moon?

Accepted Answer

$$70 	imes 1.6 = 112\,\mathrm{N}$$

Question 11

A 10 kg box is at rest on a horizontal surface. What is the normal force acting on the box?

Accepted Answer

$$F_N = mg = 10 	imes 9.8 = 98\,\mathrm{N}$$

Question 12

Which of the following is the correct expression for Newton's Law of Universal Gravitation?

Accepted Answer

$$F = G \frac{m_1$ m_2$}{r^2$}$$

Question 13

A 3 kg object is moving in a circle of radius 2 m at a speed of 4 m/s. What is the required centripetal force?

Accepted Answer

$$F_c = m \frac{v^2$}{r} = 3 	imes \frac{16}{2} = 24\,\mathrm{N}$$

Question 14

If the net force on an object is zero, which of the following statements must be true?

Accepted Answer

The object is either at rest or moving with constant velocity.

Question 15

A 2 kg mass is attached to a string and swung in a vertical circle of radius 1.5 m. What is the minimum speed at the top of the circle to keep the string taut?

Accepted Answer

$$v = \sqrt{g r} = \sqrt{9.8 	imes 1.5} \approx 3.84\,\mathrm{m/s}$$

Question 16

Which of the following best describes the relationship between frequency $$f$$ and period $$T$$ for an object in uniform circular motion?

Accepted Answer

$$f = \frac{1}{T}$$

Forces, Newton's Laws, and Circular Motion: Study Notes

스터디 가이드 - 연습 문제

학습 가이드 - 플래시카드