Q: A person pushes a box 3 m across a floor with a force of 20 N at an angle of 60° above the horizontal. What is the work done by the person?

$$W = 20 \times 3 \times \cos 60^\circ = 30\ \mathrm{J}$$

Q: A 0.5 kg ball is dropped from a height of 10 m. Ignoring air resistance, what is its speed just before hitting the ground?

$$v = \sqrt{2gh} = \sqrt{2 \times 9.8 \times 10} \approx 14\ \mathrm{m/s}$$

Q: A 3 kg block slides down a rough incline, losing 20 J of mechanical energy to friction. If it starts from rest at a height of 5 m, what is its speed at the bottom?

$$v = \sqrt{2(3 \times 9.8 \times 5 - 20)/3} \approx 7.2\ \mathrm{m/s}$$

Question 1

A 2 kg block is pulled to the right with a constant force of 10 N on a frictionless surface. What is the acceleration of the block?

Accepted Answer

$$a = 5\ \mathrm{m/s^2$}$$

Question 2

A 3 kg object is acted upon by two forces: $$\vec{F}_1 = 4\ \mathrm{N}$$ east and $$\vec{F}_2 = 3\ \mathrm{N}$$ north. What is the magnitude of the object's acceleration?

Accepted Answer

$$a = 1.67\ \mathrm{m/s^2$}$$

Question 3

Which of the following best defines the acceleration due to gravity $$g at $$the surface of a planet of mass $$M$$ and radius $$R$$?

Accepted Answer

$$g = \dfrac{GM}{R^2$}$$

Question 4

A 70 kg astronaut weighs less on the Moon than on Earth. Which statement best explains why?

Accepted Answer

The Moon has less mass and a smaller radius, so $$g is $$smaller.

Question 5

A 5 kg box rests on a horizontal surface. The coefficient of static friction is 0.4. What is the maximum force that can be applied horizontally before the box starts to move?

Accepted Answer

$$F_{max} = 20\ \mathrm{N}$$

Question 6

Two blocks, $$m_1 = 2$$\ \mathrm{kg}$$ and m_2$ = 3\ \mathrm{kg}$$, are connected by a light string over a frictionless pulley. $$m_2$$ hangs vertically while $$m_1$$ rests on a frictionless table. What is the acceleration of the system?

Accepted Answer

$$a = 5.88\ \mathrm{m/s^2$}$$

Question 7

A car of mass $$m$$ travels at speed $$v$$ around a banked curve of radius $$r$$ with banking angle $$	heta. If $$there is no friction, what is the correct expression for the speed at which the car can travel without sliding?

Accepted Answer

$$v = \sqrt{rg	an	heta}$$

Question 8

A skydiver of mass 80 kg falls through the air and eventually reaches terminal speed. Which statement best describes terminal speed?

Accepted Answer

It is the speed at which the upward force of air resistance equals the downward force of gravity.

Question 9

The resistive force on a falling object is given by $$F_{resist} = bv$$, where $$b is a $$constant. What is the expression for the terminal speed $$v_t$$?

Accepted Answer

$$v_t = \dfrac{mg}{b}$$

Question 10

A force $$\vec{F}$$ acts on an object, causing a displacement $$\vec{d}. $$Which equation correctly defines the work done by the force?

Accepted Answer

$$W = \vec{F} \cdot \vec{d}$$

Question 11

A person pushes a box 3 m across a floor with a force of 20 N at an angle of 60° above the horizontal. What is the work done by the person?

Accepted Answer

$$W = 20 	imes 3 	imes \cos 60^\circ = 30\ \mathrm{J}$$

Question 12

A 0.5 kg ball is dropped from a height of 10 m. Ignoring air resistance, what is its speed just before hitting the ground?

Accepted Answer

$$v = \sqrt{2gh} = \sqrt{2 	imes 9.8 	imes 10} \approx 14\ \mathrm{m/s}$$

Question 13

A 2 kg block is attached to a horizontal spring (spring constant $$k = 100\ \mathrm{N/m}) $$and is compressed 0.1 m from equilibrium. If the block is released from rest and there is no friction, what is its speed as it passes through equilibrium?

Accepted Answer

$$v = 2.24\ \mathrm{m/s}$$

Question 14

A 1 kg object is thrown vertically upward with an initial speed of 20 m/s. Ignoring air resistance, what is the maximum height reached?

Accepted Answer

$$h = \dfrac{v^2$}{2g} = \dfrac{400}{19.6} \approx 20.4\ \mathrm{m}$$

Question 15

A 0.2 kg object is moving at 5 m/s. What is its kinetic energy?

Accepted Answer

$$KE = \dfrac{1}{2}mv^2$ = 2.5\ \mathrm{J}$$

Question 16

A 3 kg block slides down a rough incline, losing 20 J of mechanical energy to friction. If it starts from rest at a height of 5 m, what is its speed at the bottom?

Accepted Answer

$$v = \sqrt{2(3 	imes 9.8 	imes 5 - 20)/3} \approx 7.2\ \mathrm{m/s}$$

Question 17

Which of the following best defines the density $$\rho of a $$material?

Accepted Answer

$$\rho = \dfrac{m}{V}$$

Question 18

A 10 kg object is suspended by a rope. What is the tension in the rope if the object is at rest?

Accepted Answer

$$T = 98\ \mathrm{N}$$

Question 19

A 0.5 kg ball is attached to a string and swung in a horizontal circle of radius 2 m at a constant speed of 4 m/s. What is the tension in the string?

Accepted Answer

$$T = 8\ \mathrm{N}$$

Exam 2 Study Guide: Forces, Gravitation, Circular Motion, Work, and Energy

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