Week 1 Homework

Assigned Readings: please see the syllabus for full details

Homework Problems | Approximate Answer | Student Responsible for Posting Solution |
---|---|---|

[1] A horizontal force of 120 N is required to push a bookcase across the floor at constant velocity. (a) What is the net force acting on the bookcase? (b) How much is the friction force that acts on the sliding bookcase? (c) How much friction acts on the bookcase when it is at rest on a horizontal surface without being pushed? | (a) 0 N (b) 120 N (c) 0 N |
Allen, Timothy |

[2] Calculate the acceleration of a hamster if it increases its velocity from rest to 10 m/s in two seconds. | 5.0 m/s^2 | Ambrose, Amanda |

[3] A school bus slows to a stop with an average acceleration of -2.0 m/s^2. Calculate how much time it takes for the bus to slow down from 10 m/s to a complete stop. | 5.0 s | Atilano, Joseph |

[4] A small airplane starts from rest at one end of a runway and accelerates at 4.0 m/s^2 for 15 s before takeoff. (a) What is the speed at takeoff? (b) What is the average speed of the plane down the runway? (c) What distance did the plane travel before takeoff? | 60 m/s 30 m/s 450 m |
Dr. Bob |

[5] Madison pushes with a 160 N horizontal force on a 20 kg crate of coffee resting on a warehouse floor. The force of friction on the crate is 80 N. Calculate the acceleration. | 4.0 m/s^2 | Ballesteros, Melanie |

[6] If you stand next to a wall on a frictionless skateboard and push the wall with the force of 40 N, how hard does the wall push back on you? If your mass is 80 kg, calculate your acceleration. | (a) 40 N (b) 0.5 m/s^2 |
Bessinger-Sanchez, Earl Justine |

[7] A firefighter of mass 80 kg slides down a vertical pole with an acceleration of 4 m/s^2. Calculate the force of friction that acts on the firefighter. | 464 N | Dr. Bob |

[8] An astronaut lands on a planet that has the same mass as Earth but twice the diameter. How does the astronaut's weight differ from that on Earth? | weight on other planet is 1/4 the weight on Earth | Burns, Alisha |

[9] What is the gravitational force of attraction between a 150,000,000 kg block of granite and a 200,000,000 kg rock if they are 18.0 meters apart? | F = 6179 N using G = 6.673 x 10^-11 |
Campbell, Lisa |

[10] The top speed of a car is limited by air resistance. When
the force of air resistance equals the force delivered by the
car its acceleration is zero and it moves at a constant velocity. The force of air resistance can be given by F = D v ^{2}, where D is an overall drag-factor and v is the velocity of the car.What is the top speed of a sports car if it can deliver a maximum force of 5502 N against air resistance and its Drag factor is 0.6792 kg/m ? |
top speed is 90.0 m/s (~198 mph) |
Dr. Bob |

Week 2 Homework

Assigned Readings: please see the syllabus for full details

Homework Problems | Approximate Answer | Student Responsible for Posting Solution |
---|---|---|

[1] At some point in its orbit, an asteroid is moving with a speed of 20 kilometers per second. Determine the kinetic energy of the asteroid assuming it has a mass of 1000 kilograms. Be sure to use the correct units in your calculation. | 2.00 x 10^11 J | Cox, Jonathan |

[2] Using the work-energy theorem, calculate the work needed to bring a car, moving at 90.0 m/s (~198 mph) and having a mass of 1200 kg, to rest. Next, if the car's brakes supply a force of 8600 N resisting the motion, what distance will it take to stop? Hint: use the other work definition for second part. | −4,860,000 J 565 m |
Culbreath, Emerald |

[3] Bernie dives from atop a tall flagpole into a swimming pool below. His potential energy at the top is 10,000 J. What is his kinetic energy when his potential energy is 4000 J at some point during his fall? | 6000 J | Dickey, Candice |

[4] What is Bernie's velocity when his potential energy is 4000 J? Assume Bernie's mass is 80 kg. | 12.2 m/s | Doss, Michael |

[5] What is Bernie's height when his kinetic energy is 6000 J? Assume Bernie's mass is 80 kg. | 5.10 m | Eisel, Kara |

[6] Calculate how much power is needed by a weightlifter when lifting a 60 kg barbell a vertical distance of 1.2 m in a time interval of 1.5 seconds. | 470.4 W | Fuller, Patrick |

[7] A 12 kg piece of metal displaces 2000 cm^3 of water when submerged. Calculate its density in grams per cubic centimeter. How does this density compare with the density of water? | 6.0 g/cm^3 | Goldson, Sheree |

[8] A merchant sells you a solid-gold, 1 kg statue for a very reasonable price. You wonder whether you got a bargain, so you lower the statue into a container of water and measure the volume of displaced water. What is the volume of water you would expect to be displaced for 1 kg of pure gold? | 51.8 cm^3 | Jones, Michelle |

[9] A rock is thrown with a speed of 45 m/s. Determine its kinetic energy assuming the mass of the rock is 500 g. Be sure to use the correct units in your calculation. | 506.25 J | Lillington, Norman |

[10] Using scientific notation, numerically evaluate the expression below. Do this problem without using a calculator. See the "Scientific Notation Basics" link under Dr. Bob's Extra Stuff for details. Show all of your steps. (8 x 10^6) (2 x 10^-3) |
1.6 x 10^4 or 16,000 |
Marlowe, Tara |

[11] Using scientific notation, numerically evaluate the expression below. Do this problem without using a calculator. See the "Scientific Notation Basics" link under Dr. Bob's Extra Stuff for details. Show all of your steps. (8 x 10^6) / (2 x 10^-3) |
4 x 10^9 or 4,000,000,000 |
Norris, Jasmine |

Week 3 Homework

Assigned Readings: please see the syllabus for full details

Homework Problems | Approximate Answer | Student Responsible for Posting Solution |
---|---|---|

[1] Calculate the number of calories required to raise the temperature of 30 g of water from 22°C to 30°C. The specific heat capacity for water is one calorie per gram per degree Celsius. | 240 cal | TBA |

[2] Determine the amount of heat in joules required to raise 30 g of aluminum from 22°C to 30°C. Specific heat capacity for aluminum is 0.22 calories per gram per degree Celsius. | 221 J | TBA |

[3] Determine the quantity of heat needed to raise the temperature of a 10 kg piece of steel from 0°C to 100°C. Compare this to the amount of heat needed to raise the temperature of the same mass of water through the same temperature difference. The specific heat capacity of steel is 450 J per kilogram per degree Celsius. | 450,000 J for steel 4,186,000 J for water |
TBA |

[4] The specific heat capacity of ice is about 0.5 cal per gram per degree Celsius. Suppose it remains at that value all the way to absolute zero. Determine the quantity of heat needed to change a 1 g ice cube at absolute zero to 1 g of boiling water. Hint: you will need to do this problem in three parts (a) heat needed to change temperature from absolute zero to melting temperature of water, (b) heat needed to melt the ice, (c) heat needed to change temperature from melting temperature to boiling temperature. The final answer is determined by adding the results from parts (a), (b), and (c). | 316.5 cal | TBA |

[5] Calculate how many grams of ice at 0°C would be melted by 100 g of 100°C steam. Hint: heat will be transferred from the steam to the ice in two processes: (a) the steam will condense into liquid, and (b) that liquid will transfer heat until it is at the freezing point of water. Note that for water: L_{f} = 80 cal/g, and L_{v} = 540 cal/g |
800 g | TBA |

[6] The heat of vaporization of ethyl alcohol is about 200 cal per gram. If 4 kg of this refrigerant were allowed to vaporize in a refrigerator, how many grams of 0°C water could be converted into ice? Note that for water: L_{f} = 80 cal/g |
10,000 g | TBA |

[7] Two pellets, each with a charge of 10^-6 C, are located 3 cm apart. Determine the size of the electric force between them. | 10 N | TBA |

[8] Two point charges are separated by 4 cm. The attractive force between them is 20 N. Determine what the force is when they are separated by 8 cm. Explain how you are able to solve this problem without knowing the magnitude of each charge. | 5.0 N | TBA |

[9] The electric potential difference between a storm cloud and the ground is 100 million volts. If a charge of 2.0 C flashes in a bolt from the cloud to the ground, determine the change in potential energy of that charge. | 2.0 x 10^8 J | TBA |

Week 4 Homework

Assigned Readings: please see the syllabus for full details

Homework Problems | Approximate Answer | Student Responsible for Posting Solution |
---|---|---|

[1] A device in a 120 V circuit has a current rating of 20 Amp. Determine the resistance of this device. | 6.0 Ω | TBA |

[2] Determine the current that flows in a 300 watt lightbulb when connected to 120 V circuit. | 2.5 A | TBA |

[3] Determine the resistance of the 300 watt lightbulb in the previous problem. | 48 Ω | TBA |

[4] A video game console requires 6.00 V to operate correctly. A transformer allows the device to be powered from 120 V outlet. If the primary has 500 turns, determine how many turns should be in the secondary. | 25 | TBA |

[5] For the video game problem presented before, determine the output current if the input current is 0.1 A. Determine the resistance of this device. | 2.0 A 3.0 Ω |
TBA |

[6] For a particular patient, a nurse counts 72 heartbeats in one minute. Determine the frequency and period of heartbeats for this patient. | P = 0.83 s f = 1.2 Hz |
TBA |

[7] Microwave ovens typically cook food using microwaves with the frequency of about 3.00 GHz (1 GHz = 10^9 Hz). Determine the wavelength of these microwaves. | 0.10 m | TBA |

[8] Electrons on a radio broadcasting tower were forced to oscillate up and down an antenna 535,000 times each second. Determine the wavelength of the radio waves that are produced. | 561 m | TBA |

[9] Blue-green light has a frequency of about 6.00 x 10^14 Hz. Determine its wavelength. Compare this wavelength to the size of an atom (about 10^-10 m) by calculating the ratio: wavelength/(atom size). | 5 x 10^-7 m 5000 times larger |
TBA |

Week 5 Homework

Assigned Readings: please see the syllabus for full details

Homework Problems | Approximate Answer | Student Responsible for Posting Solution |
---|---|---|

[1] What are the atomic number, mass number, and element formed when polonium-218 emits a beta particle? What are they if the polonium emits an alpha particle? Please see my examples in Dr. Bob's Extra Stuff and use the notation shown there. | At-218 Pb-214 |
TBA |

[2] The isotope cesium-137 has a half-life of 30 years. It is a by product of nuclear power plants. How long will it take this isotope to decay to 1/16 of its original amount? | 120 years | TBA |

[3] A certain radioactive substance has a half-life of 1 hour. If you start with a 1024 g sample at noon, how much is left at 3:00 PM? At 6:00 PM? At 10:00 PM? | 128 g 16 g 1 g |
TBA |

[4] Some asteroid fragments end up on the surface of Earth. These fragments can be radioactive. What is the chief cause of radioactivity? Given a radiation detector that can ONLY measure the amount of radiation, how could you determine which type of radiation was being emitted? | - | TBA |

[5] In nuclear fission and fusion reactions mass is converted into energy. The average person in US uses around 100,000,000 J of energy per year. (a) Calculate the yearly energy consumption for a US population of 300 million. (b) Using Einstein's famous formula, E = m c^2, calculate the energy that would be released if a 60 kg person were converted entirely into energy. (c) How many years would this amount of energy support a population of 300 million? |
3.0 x 10^16 J 5.4 x 10^18 J 180 years |
TBA |

[6] The isotope lithium-7 has a mass of 7.0160 amu, and the isotope lithium-6 has a mass of 6.0151 amu. 92.58% of all lithium atoms found in nature are lithium-7 and 7.42% are lithium-6. Use this information to calculate the atomic mass of lithium. | 6.941 amu | TBA |

[7] You are given samples of the elements argon, bromine, and sulfur. Which of these elements is most similar to chlorine? Defend your answer using your knowledge of the periodic table. | - | TBA |

[8] What is the formula for the ionic compound formed by each pair of ions? K ^{+} and Cl^{−}Mg ^{2+} and Cl^{−}Mg ^{2+} and Se^{2−}Mg ^{2+} and N^{3−}Al ^{3+} and S^{2−} |
KCl MgCl _{2}MgSe Mg _{3}N_{2}Al _{2}S_{3} |
TBA |

Week 6 Homework

Assigned Readings: please see the syllabus for full details

Homework Problems | Approximate Answer | Student Responsible for Posting Solution |
---|---|---|

[1] Balance the chemical equations shown below. Show your work and explain what you're doing step-by-step. Fe + O _{2} → Fe_{2}O_{3}Cl _{2} + KBr → Br_{2} + KCl |
- | TBA |

[2] Balance the chemical equations shown below. Show your work and explain what you're doing step-by-step. H _{2} + N_{2} → NH_{3}CH _{4} + O_{2} → CO_{2} + H_{2}O |
- | TBA |

[3] Determine the number of carbon atoms in a 1-carat pure diamond that has a mass of 0.20 g. | 1.0 x 10^22 carbon atoms | TBA |

[4] What is the mass of a water molecule, H_{2}O, in atomic mass units? What is the mass of 1.00 mole of water? How many moles of water do you have if you are given 63.0 g of water? |
18.0 u 18.0 g 3.50 |
TBA |

[5] What is the mass of a sucrose molecule (table sugar), C_{12}H_{22}O_{11}, in atomic mass units? What is the mass of 1.00 mole of sucrose? How many moles of sucrose do you have if you are given 63.0 g of sucrose? |
342.3 u 342.3 g 0.184 |
TBA |

[6] Small samples of oxygen gas needed in the laboratory can be generated by a number of simple chemical reactions, such as 2 KClO _{3} → 2 KCl + 3 O_{2}According to this balanced chemical equation, how many moles of oxygen gas are produced from the reaction of one mole of KClO _{3}? How many grams of O_{2} are produced? |
1.5 moles of O_{2}48 g of O _{2} |
TBA |

[7] Small samples of oxygen gas needed in the laboratory can be generated by a number of simple chemical reactions, such as 2 KClO _{3} → 2 KCl + 3 O_{2}According to this balanced chemical equation, how many moles of oxygen gas are produced from the reaction of 245 grams of KClO _{3}? How many grams of O_{2} are produced? |
3.0 moles of O_{2}96 g of O _{2} |
TBA |

Week 7 Homework

Assigned Readings: please see the syllabus for full details

Homework Problems | Approximate Answer | Student Responsible for Posting Solution |
---|---|---|

[1] As the result of a chemical reaction, 19.8 g of CO_{2} gas is produced. Using the ideal gas law, determine the volume of gas produced when the pressure is 1.00 atmosphere and the temperature is 33.0°C. |
11.3 L ~3 gallons |
TBA |

[2] Determine the molarity of a solution that consists of 4.00 g of NaOH dissolved in 250 mL of water. | 0.400 M | TBA |

[3] Using the Brønsted-Lowry definition of acids and bases, identify each reactant in the reactions below as an acid or base. Explain how you determined your answers in detail. H _{3}O^{+} + Cl^{-} → H_{2}O + HClH _{2}PO_{4}^{-} + H_{2}O → H_{3}O^{+} + HPO_{4}^{2-}HSO _{4}^{-} + H_{2}O → OH^{-} + H_{2}SO_{4}O ^{2-} + H_{2}O → OH^{-} + OH^{-} |
- | TBA |

[4] Using the ion-product of water relationship, determine the hydroxide-ion concentration in a solution if the hydronium-ion concentration is 4.00 x 10^-10 molar. Is this an acid or base solution? | [OH-] = 2.50 x 10^-5 M base |
TBA |

[5] A solution has an hydronium-ion concentration of 2.5 x 10^-3 M. What is its pH? Is this an acid or base solution? | pH = 2.60 acid |
TBA |

[6] A solution has an pH = 5.00, so what is its hydronium-ion concentration? What is its hydroxide-ion concentration? Is this an acid or base solution? | [H_{3}O+] = 10^-5[OH-] = 10^-9 acid |
TBA |

Week 8 Homework

Homework Review for Final Exam Prep

Homework Problems | Approximate Answer | Student Responsible for Posting Solution |
---|---|---|

[1] Find the net force produced by a 30 N force and a 10 N force in each of these cases: both forces act in the same direction, the two forces act in opposite directions. Calculate the acceleration for both cases if the net force acts on a 20 kg crate. | (a) Fnet = 40N a = 2.0 m/s^2 (b) Fnet = 20N a = 1.0 m/s^2 |
TBA |

[2] Consider a pair of planets for which the distance between them is increased by a factor of three. Show what happens to the force of attraction between these two planets. | New force is 1/9 size of old force | TBA |

[3] A bald eagle dives from a rocky outcrop. Its potential energy at the top is 18,000 J. What is its kinetic energy when its potential energy is 8000 J at some point during his dive? What is eagle's speed and height at that point in its dive? Assume the eagle's mass is 6.00 kg. | 10,000 J 57.74 m/s 136.05 m |
TBA |

[4] A 1.84 kg cube of ice measures 12.6 cm on its edge. What is the mass in grams? What is the volume in cubic centimeters?. Calculate its density in grams per cubic centimeter. How does this density compare with the density of water? | 1840 g 2000 cm^3 0.92 g/cm^3 less |
TBA |

[5] Determine the amount of heat required (in calories and joules) to raise 230 g of a liquid from 22°C to 28°C. The specific heat capacity for this liquid is 0.30 calories per gram per degree Celsius. | 414 cal 1733 J |
TBA |

[6] Determine the amount of heat that would need to be removed to freeze the liquid in the previous problem (assuming the liquid is at its freezing temperature). Determine the amount of heat that would need to be added to boil the liquid in the previous problem (assuming the liquid is at its boiling temperature). Given: Lf = 2.9 cal/g; Lv = 13 cal/g. |
667 cal 2990 cal |
TBA |

[7] A solution has an pH = 9.00, so what is its hydronium-ion concentration? What is its hydroxide-ion concentration? Is this an acid or base solution? | [H3O+] = 1.00 x 10^-9 molar [OH-] = 1.00 x 10^-5 molar base |
TBA |

[8] Two ping-pong balls, each with a positive charge of 2.5 x 10^-5 C, are located 9.0 cm apart. Determine the size of the electric force between them. Would this be enough force to support a 70 kg person against the downward force of gravity? | 694 N yes because the downward force of gravity is 686 N |
TBA |

[9] A phone-charger requires 5.00 V to operate. A transformer allows the device to be powered from an overseas 240 V outlet. If the primary has 480 turns, determine how many turns should be in the secondary. What is the resistance of the phone-charger if it draws a current of 0.25 amp? | 10 turns 20 ohms |
TBA |

[10] Molecular hydrogen and molecular oxygen are burned in rockets (this was the fuel for the Space Shuttle's main engines). This reaction results in water being produced (in the form of super-heated steam) and an enormous amount of energy. The reaction is shown below.
2 H _{2} is 6.00 g of H_{2}? How many moles of water are produced when 6.00 g of H_{2} react? How many grams of water are produced when 6.00 g of H_{2} react? |
2.97 2.97 53.49 g |
TBA |