Week 1 Homework

Assigned Readings: please see the syllabus for full details

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

[1] Find the net force produced by a 30 N force and a 20 N force in each of these cases: (a) both forces act in the same direction. (b) the two forces act in opposite directions. | (a) 50 N (b) 10 N |
Barrett, Chad |

[2] 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 |
Beaver, Brandon |

[3] Gravitational force on the Moon is only one sixth that of the gravitational force on Earth. What would be the weight of the 10 kg object on the Moon and on Earth? What would be its mass on the Moon and on Earth? | (a) 98.0 N (b) 16.3 N (c) 10 kg |
Bell, Joseph |

[4] A hockey puck slides across the ice at a constant velocity. Is the sliding puck in equilibrium? Why or why not? | Yes | Blair, Denise |

[5] Correct your friend who says, "The proposed California Suntrain can easily round a curve at a constant velocity of 45 m/s." | - | Cervas, Evangeline |

[6] 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 | Cheung, Yoon |

[7] 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 | Childs, Tyler |

[8] 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 |

Week 2 Homework

Assigned Readings: please see the syllabus for full details

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

[1] 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 | Clements, Davin |

[2] A rocket of mass 100,000 kg undergoes an acceleration of 2 m/s^2. What is the net force? | 200,000 N | Clements, Justin |

[3] 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 |
Davis, Davina |

[4] 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. | use g = 9.8 m/s^2 then friction force is 464 N |
Dr. Bob |

[5] 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 | Dunlap, Sharleeta |

[6] Consider a pair of planets for which the distance between them is decreased by a factor of five. Show what happens to the force of attraction between these two planets. | force of attraction is 25 times more | Elder, Symone |

[7] 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 = 6176 N | Dr. Bob |

[8] The top speed of a car is limited by air resistance. When
the force of air resistance equals the force delivered by the
car, 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 a 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 |

[9] 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 |
Endale, Michael |

[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) |
4 x 10^9 or 4,000,000,000 |
Forna, Amadu |

Week 3 Homework

Assigned Readings: please see the syllabus for full details

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

[1] At a baseball game a ball of mass 0.15 kg moving at a speed of 30 m/s is caught by a fan. (a) Determine the impulse needed to bring the ball to rest. (b) If the ball is stopped in 0.02 seconds, determine the average force needed to stop the ball. | (a) 4.5 N • s (b) 225 N |
TBA |

[2] Judy (mass 40 kg), standing on slippery ice, catches her dog (mass 15 kg) leaping toward her at 3.0 m/s. Use conservation of momentum that to determine the speed of Judy and her dog after the catch. | 0.82 m/s | TBA |

[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 | TBA |

[4] What is Bernie's velocity when his kinetic energy is 6000 J? Assume Bernie's mass is 80 kg. | 12.2 m/s | TBA |

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

[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 | TBA |

[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 | TBA |

[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 | TBA |

[9] 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 | TBA |

Week 4 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 4,187,000 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 |

Week 5 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. Please show your work and explain what you're doing step-by-step. Fe + O _{2} → Fe_{2}O_{3}H _{2} + N_{2} → NH_{3}Cl _{2} + KBr → Br_{2} + KClCH _{4} + O_{2} → CO_{2} + H_{2}O |
- | TBA |

[2] 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 |

[3] 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 |

[4] 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 |

[5] Identify each substance in these reactions as an acid or base. You should identify everything on both sides of the reaction. Be sure to explain how you determined your answers. 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 |

[6] 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 |

[7] 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 6 Homework

Assigned Readings: please see the syllabus for full details

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

[1] 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 |

[2] 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 |

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

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

[5] 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 |

[6] 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 |

Week 7 Homework

Assigned Readings: please see the syllabus for full details

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

[1] 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 |

[2] 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 |

[3] 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 |

[4] 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 |

[5] What are the atomic number and the atomic mass of the 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 |

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

[7] 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 |

[8] Some asteroid fragments are large enough to not completely burn up in the atmosphere and they end up on the surface of the Earth. These fragments can be radioactive. What is the chief cause of radioactivity? If you had a radiation detector that could measure the amount of radiation -- but not the type of radiation -- how could you determine which type of radiation was being emitted? | - | 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] Determine the hydroxide-ion concentration in a solution if the hydronium-ion concentration is 1.00 x 10^-10 molar. What is the pH of this solution? Is this an acid or base solution? | [OH-] = 1.00 x 10^-4 molar pH = 10.00 base |
TBA |

[8] 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 |

[9] 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 |

[10] 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 |

[11] 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 |
0.5 mole 2.02 g 32.00 g 18.02 g |
TBA |

[12] 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 |