Physics
Physics
1st Edition
Walker
ISBN: 9780133256925
Table of contents
Textbook solutions

All Solutions

Page 206: Lesson Check

Exercise 27
Step 1
1 of 4
In this problem, we are asked what happens to the kinetic energy of an object when the speed doubles and triple.
Step 2
2 of 4
From the definition of the kinetic energy, we have

$$
begin{align*}
KE &= frac{1}{2}mv^{2} \
implies KE &propto v^{2}
end{align*}
$$

The kinetic energy is proportional to the square of the speed.

Step 3
3 of 4
When the speed is increased by a factor of $2$, the kinetic energy must be $textbf{increased by a factor of $4$.}$
Step 4
4 of 4
When the speed is increased by a factor of $3$, the kinetic energy must be $textbf{increased by a factor of $9$.}$
Exercise 28
Step 1
1 of 2
In this problem, we explain what happens to the kinetic energy of an object if the work done is positive, such that $W > 0$.
Step 2
2 of 2
Using work-energy theorem, we have

$$
begin{align*}
Delta KE &= W \
Delta KE &> 0
end{align*}
$$

The change in kinetic energy is positive, so the final kinetic energy must be greater than the initial kinetic energy. The kinetic energy $textbf{increases}$.

Exercise 29
Step 1
1 of 3
In this problem, a pitcher throws a baseball with speed $v = 40~mathrm{m/s}$ and the catcher stops it in her glove. We find the sign of the work done on the ball.
Step 2
2 of 3
The initial kinetic energy is positive. Since the ball stops, its final kinetic energy is zero. The final kinetic energy is less than the initial. The change in kinetic energy is negative
$$
Delta KE < 0
$$
Step 3
3 of 3
Using work-energy theorem, we have

$$
begin{align*}
W &= Delta K \
W &< 0
end{align*}
$$

The work done on the ball by the catcher is $textbf{negative}$.

Exercise 30
Step 1
1 of 3
In this problem, we compare the change in potential energy when a box is lifted by $h = 1~mathrm{m}$ off the surface of the Earth and the Moon.
Step 2
2 of 3
The mass of the object and the change in elevation is the same for both cases. The change in potential energy is

$$
begin{align*}
Delta PE_text{gravity} &= mg Delta h \
Delta PE_text{gravity} &= left( m Delta h right) g \
Delta PE_text{gravity} &propto g
end{align*}
$$

The change in gravitational potential energy is proportional to the acceleration due to gravity in the surface.

Step 3
3 of 3
Since the acceleration due to gravity on the Earth is greater than the acceleration due to gravity on the Moon, the change in potential energy is $textbf{not the same}$.
Exercise 31
Step 1
1 of 3
In this problem, we find what happens to the potential energy of the spring when the amount of stretch is doubled.
Step 2
2 of 3
From the definition of spring potential energy, we have
$$
begin{aligned}
PE_text{spring} &= frac{1}{2}kx^{2} \
implies PE_text{spring} &propto x^{2}
end{aligned}
$$
The spring potential energy is proportional to the square of the amount of stretching.
Step 3
3 of 3
When the amount of stretching is increased by a factor of $2$, the potential energy must **increase by a factor of** $4$.
Exercise 32
Step 1
1 of 3
In this problem, a bullet has mass $m = 9.50 times 10^{-3}~mathrm{kg}$ and speed $v = 1.30 times 10^{3}~mathrm{m/s}$. We calculate the kinetic energy.
Step 2
2 of 3
The kinetic energy, as defined, is

$$
begin{align*}
KE &= frac{1}{2}mv^{2} \
&= frac{1}{2} left( 9.50 times 10^{-3}~mathrm{kg} right) left( 1.30 times 10^{3}~mathrm{m/s} right)^{2} \
&= 8027.50000~mathrm{J} \
KE &= boxed{ 8.03 times 10^{3}~mathrm{J} }
end{align*}
$$

Result
3 of 3
$$
KE = 8.03 times 10^{3}~mathrm{J}
$$
Exercise 33
Step 1
1 of 3
In this problem, a volleyball of mass $m = 0.27~mathrm{kg}$ has kinetic energy $KE = 7.8~mathrm{J}$. We calculate its speed.
Step 2
2 of 3
From the definition of the kinetic energy, we have

$$
begin{align*}
KE &= frac{1}{2}mv^{2} \
v^{2} &= frac{2KE}{m} \
implies v &= sqrt{frac{2KE}{m}} \
&= sqrt{frac{2 left( 7.8~mathrm{J} right)}{0.27~mathrm{kg}}} \
&= 7.60117~mathrm{m/s} \
v &= boxed{ 7.6~mathrm{m/s} }
end{align*}
$$

Result
3 of 3
$$
v = 7.6~mathrm{m/s}
$$
Exercise 34
Step 1
1 of 4
In this problem, a runner of mass $m = 73~mathrm{kg}$ accelerations from rest $v_text{i} = 0$ to a speed of $v_text{f} = 7.5~mathrm{m/s}$. We calculate the work required for this activity.
Step 2
2 of 4
First, we find the initial and final kinetic energy of the runner. We have

$$
begin{align*}
KE_text{i} &= frac{1}{2}mv_text{i}^{2} \
KE_text{f} &= frac{1}{2}mv_text{f}^{2} \
end{align*}
$$

Step 3
3 of 4
We now use the work-energy theorem. We have

$$
begin{align*}
W &= Delta KE = KE_text{f} – KE_text{i} \
&= frac{1}{2}mv_text{f}^{2} – frac{1}{2}mv_text{i}^{2} \
&= frac{1}{2}m left[v_text{f}^{2} – v_text{i}^{2} right] \
&= frac{1}{2} left( 73~mathrm{kg} right) left[ left( 7.5~mathrm{m/s} right)^{2} – 0 right] \
&= 2053.125~mathrm{J} \
W &= boxed{ 2100~mathrm{J} }
end{align*}
$$

Result
4 of 4
$$
W = 2100~mathrm{J}
$$
Exercise 35
Step 1
1 of 3
In this problem, a pinecone of mass $m = 0.14~mathrm{kg}$ is at height $h = 16~mathrm{m}$ above the ground. We calculate the gravitational potential energy. We use $g = 9.81~mathrm{m/s^{2}}$.
Step 2
2 of 3
From the definition, we have
$$begin{aligned}
PE_text{gravity} &= mgh \
&= left( 0.14~mathrm{kg} right)left( 9.81~mathrm{m/s^{2}} right) left( 16~mathrm{m} right) \
&= 21.9744~mathrm{J} \
PE_text{gravity} &= boxed{ 22~mathrm{J} }
end{aligned}$$
Result
3 of 3
$$PE_text{gravity} = 22~mathrm{J} $$
Exercise 36
Solution 1
Solution 2
Step 1
1 of 4
In this problem, it takes $F = 13~mathrm{N}$ to stretch a certain spring by $x = 9.5 times 10^{-2}~mathrm{m}$. We calculate the potential energy stored in the spring.
Step 2
2 of 4
First, we calculate the spring constant of the spring. From the definition, we have

$$
begin{aligned}
F &= kx \
implies k &= frac{F}{x} tag{1}
end{aligned}
$$

Step 3
3 of 4
Substituting this into the equation for potential energy, we have

$$
begin{aligned}
PE &= frac{1}{2}kx^{2} \
&= frac{1}{2} left( frac{F}{x} right)x^{2} \
&= frac{1}{2}Fx \
&= frac{1}{2} left( 13~mathrm{N} right) left( 9.5 times 10^{-2}~mathrm{m} right) \
&= 0.6175~mathrm{J} \
PE &= boxed{ 0.62~mathrm{J} }
end{aligned}
$$

Result
4 of 4
$PE = 0.62~mathrm{J}$
Step 1
1 of 4
To solve the problem, first, we need to compute the spring constant using the equation

$$
F = kx
$$

We will also convert the value of x from $cm$ to $m$.

$$
x = 9.5cm = 0.095m
$$

Step 2
2 of 4
Rearranging the equation and substituting the values to obtain the spring constant,

$$
k = dfrac{F}{x} = dfrac{13N}{0.095m} = 136.84N/m
$$

Step 3
3 of 4
Now that we have the spring constant, we can compute the potential energy in the spring

$$
PE = dfrac{1}{2} kx^2 = dfrac{1}{2} (136.84N/m)(0.095m)^2
$$

$$
PE = 0.62J
$$

Result
4 of 4
$$
PE = 0.62J
$$
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Chapter 1: Introduction to Physics
Section 1.1: Physics and the Scientific Method
Section 1.2: Physics and Society
Section 1.3: Units and Dimensions
Section 1.4: Basic Math for Physics
Page 38: Assessment
Page 41: Standardized Test Prep
Chapter 2: Introduction to Motion
Section 2.1: Describing Motion
Section 2.2: Speed and Velocity
Section 2.3: Position-Time Graphs
Section 2.4: Equation of Motion
Page 66: Assessment
Page 71: Standardized Test Prep
Page 45: Practice Problems
Page 47: Practice Problems
Page 47: Lesson Check
Page 49: Practice Problems
Page 52: Practice Problems
Page 53: Lesson Check
Page 56: Practice Problems
Page 57: Lesson Check
Page 59: Practice Problems
Page 60: Practice Problems
Page 62: Practice Problems
Page 62: Lesson Check
Chapter 3: Acceleration and Acceleration Motion
Section 3.1: Acceleration
Section 3.2: Motion with Constant Acceleration
Section 3.3: Position-Time Graphs for Constant Acceleration
Section 3.4: Free Fall
Page 105: Assessment
Page 111: Standardized Test Prep
Chapter 4: Motion in Two Dimensions
Section 4.1: Vectors in Physics
Section 4.2: Adding and Subtracting Vectors
Section 4.3: Relative Motion
Section 4.4: Projectile Motion
Page 144: Assessment
Page 149: Standardized Test Prep
Chapter 5: Newton’s Laws of Motion
Section 5.1: Newton’s Laws of Motion
Section 5.2: Applying Newton’s Laws
Section 5.3: Friction
Page 180: Assessment
Page 187: Standardized Test Prep
Chapter 6: Work and Energy
Section 6.1: Work
Section 6.2: Work and Energy
Section 6.3: Conservation of Energy
Section 6.4: Power
Page 220: Assessment
Page 227: Standardized Test Prep
Page 191: Practice Problems
Page 193: Practice Problems
Page 196: Lesson Check
Page 196: Practice Problems
Page 199: Practice Problems
Page 201: Practice Problems
Page 203: Practice Problems
Page 204: Practice Problems
Page 205: Practice Problems
Page 206: Lesson Check
Page 209: Practice Problems
Page 211: Lesson Check
Page 213: Practice Problems
Page 214: Practice Problems
Page 215: Practice Problems
Page 216: Lesson Check
Chapter 7: Linear Momentum and Collisions
Section 7.1: Momentum
Section 7.2: Impulse
Section 7.3: Conservation of Momentum
Section 7.4: Collisions
Page 260: Assessment
Page 265: Standardized Test Prep
Chapter 8: Rotational Motion and Equilibrium
Section 8.1: Describing Angular Motion
Section 8.2: Rolling Motion and the Moment of Inertia
Section 8.3: Torque
Section 8.4: Static Equilibrium
Page 300: Assessment
Page 305: Standardized Test Prep
Page 269: Practice Problems
Page 271: Practice Problems
Page 272: Practice Problems
Page 275: Practice Problems
Page 275: Lesson Check
Page 277: Practice Problems
Page 280: Lesson Check
Page 284: Practice Problems
Page 286: Practice Problems
Page 287: Practice Problems
Page 289: Lesson Check
Page 294: Practice Problems
Page 295: Practice Problems
Page 296: Lesson Check
Chapter 9: Gravity and Circular Motion
Section 9.1: Newton’s Law of Universal Gravity
Section 9.2: Applications of Gravity
Section 9.3: Circular Motion
Section 9.4: Planetary Motion and Orbits
Page 336: Assessment
Page 341: Standardized Test Prep
Chapter 10: Temperature and Heat
Section 10.1: Temperature, Energy, and Heat
Section 10.2: Thermal Expansion and Energy Transfer
Section 10.3: Heat Capacity
Section 10.4: Phase Changes and Latent Heat
Page 378: Assessment
Page 383: Standardized Test Prep
Chapter 11: Thermodynamics
Section 11.1: The First Law of Thermodynamics
Section 11.2: Thermal Processes
Section 11.3: The Second and Third Laws of Thermodynamics
Page 410: Assessment
Page 413: Standardized Test Prep
Chapter 12: Gases, Liquids, and Solids
Section 12.1: Gases
Section 12.2: Fluids at Rest
Section 12.3: Fluids in Motion
Section 12.4: Solids
Page 446: Assessment
Page 451: Standardized Test Prep
Chapter 13: Oscillations and Waves
Section 13.1: Oscillations and Periodic Motion
Section 13.2: The Pendulum
Section 13.3: Waves and Wave Properties
Section 13.4: Interacting Waves
Page 486: Assessment
Page 491: Standardized Test Prep
Chapter 14: Sound
Section 14.1: Sound Waves and Beats
Section 14.2: Standing Sound Waves
Section 14.3: The Doppler Effect
Section 14.4: Human Perception of Sound
Page 523: Assessment
Page 527: Standardized Test Prep
Page 495: Practice Problems
Page 496: Practice Problems
Page 500: Practice Problems
Page 501: Lesson Check
Page 503: Practice Problems
Page 504: Practice Problems
Page 506: Practice Problems
Page 506: Lesson Check
Page 510: Practice Problems
Page 511: Practice Problems
Page 512: Lesson Check
Page 514: Practice Problems
Page 516: Practice Problems
Page 517: Practice Problems
Page 519: Lesson Check
Chapter 15: The Properties of Lights
Section 15.1: The Nature of Light
Section 15.2: Color and the Electromagnetic Spectrum
Section 15.3: Polarization and Scattering of Light
Page 557: Assessment
Page 563: Standardized Test Prep
Chapter 16: Reflection and Mirrors
Section 16.1: The Reflection of Light
Section 16.2: Plane Mirrors
Section 16.3: Curved Mirrors
Page 590: Assessment
Page 595: Standardized Test Prep
Chapter 17: Refraction and Lenses
Section 17.1: Refraction
Section 17.2: Applications of Refraction
Section 17.3: Lenses
Section 17.4: Applications of Lenses
Page 629: Assessment
Page 635: Standardized Test Prep
Chapter 18: Interference and Diffraction
Section 18.1: Interference
Section 18.2: Interference in Thin Films
Section 18.3: Diffraction
Section 18.4: Diffraction Gratings
Page 668: Assessment
Page 673: Standardized Test Prep
Chapter 19: Electric Charges and Forces
Section 19.1: Electric Charge
Section 19.2: Electric Force
Section 19.3: Combining Electric Forces
Page 698: Assessment
Page 703: Standardized Test Prep
Chapter 20: Electric Fields and Electric Energy
Section 20.1: The Electric Field
Section 20.2: Electric Potential Energy and Electric Potential
Section 20.3: Capacitance and Energy Storage
Page 738: Assessment
Page 743: Standardized Test Prep
Chapter 21: Electric Current and Electric Circuits
Section 21.1: Electric Current, Resistance, and Semiconductors
Section 21.2: Electric Circuits
Section 21.3: Power and Energy in Electric Circuits
Page 775: Assessment
Page 781: Standardized Test Prep
Chapter 22: Magnetism and Magnetic Fields
Section 22.1: Magnets and Magnetic Fields
Section 22.2: Magnetism and Electric Currents
Section 22.3: The Magnetic Force
Page 810: Assessment
Page 815: Standardized Test Prep
Chapter 23: Electromagnetic Induction
Section 23.1: Electricity from Magnetism
Section 23.2: Electric Generators and Motors
Section 23.3: AC Circuits and Transformers
Page 844: Assessment
Page 849: Standardized Test Prep
Chapter 24: Quantum Physics
Section 24.1: Quantized Energy and Photons
Section 24.2: Wave-Particle Duality
Section 24.3: The Heisenberg Uncertainty Principle
Page 876: Assessment
Page 881: Standardized Test Prep
Chapter 26: Nuclear Physics
Section 26.1: The Nucleus
Section 26.2: Radioactivity
Section 26.3: Applications of Nuclear Physics
Section 26.4: Fundamental Forces and Elementary Particles
Page 944: Assessment
Page 947: Standardized Test Prep