Which of the following is an example of a system where the transfer of energy is important?
The battery in your phone
The air-conditioning unit in your home
The computer you are currently using
All of the other choices are correct
A convection oven
Question 2
The Jet Aircraft industry has the highest need for
Solar Energy
Wind Energy
Low Energy Density Fuels
High Energy Density Fuels
Question 3
Why is it important to find new sources of energy?
Well-established sources of energy, like gas turbines, solar power, hydroelectric dams and wind turbines, just aren’t popular.
It isn’t; at the rate we are consuming today we will be fine for the foreseeable future.
Energy demands will continue to increase with population over the next twenty years.
Traditional forms of energy like fossil fuels aren’t as economically viable as they used to be.
Question 4
You need to fill a football with air to play with it. You know that your pump expels air at 8.2 ft/s. The needle of your pump has a radius of 4.5 millimeters. What is the volume flow rate of the air being pumped into the football?
159 cm^3 / s
276 cm^3/s
51 cm^3/s
634 cm^3/s
Question 5
A lightbulb is sitting in a lamp. You notice that the lamp becomes warm. Which of the following is true?
Your Answer Score Explanation
Work is being transferred from the lamp to the lightbulb.
Heat is being transferred from the lamp to the lightbulb.
Heat is being transferred from the lightbulb to the lamp.
Work is being transferred from the lightbulb to the lamp.
Question 6
Color is an example of an
System Property
Intensive Property
Extensive Property
None of the other options
Question 7
You need to set the oven to 450 Kelvin. What temperature do you need to set the oven to in Celsius?
177 degrees Celsius
450 degrees Celsius
350 degrees Celsius
0 degrees Celsius
Question 8
Which of the following is not true of a closed system?
A system is a closed system is the rate of mass into and out of the system is equal.
A closed system has potential energy.
In a closed system, heat and work can cross the boundaries.
A closed system has kinetic energy.
Question 9
If the temperature of a hot room with a open window is modeled by T(t) = 72 – 0.25(t). Is this a steady state condition?
No
It depends.
Yes
Question 10
A ball, with a mass of 0.06 kg, falls off a table (assume it was on the edge and started with no velocity). If the table was 1 meter off the ground, what is the velocity of the ball when it hits the ground?
1.4 m/s
0.6 m/s
1000 m/s
4.4 m/s
Question 11
Consider a jar of molasses. The empty jar weighs 20 grams and is 6 cm tall with a 3 cm diameter. A jar with molasses weights 90 g. What is the density of the molasses? Assume the molasses fills the entire jar.
1.21 g/cm^3
2.12 g/cm^3
1.65 g/cm^3
1.41 g/cm^3
Question 12
If the gauge pressure is reported as 6 atm, what is the absolute pressure?
8 atm
6 atm
7 atm
5 atm
Question 13
Consider a vertical piston/cylinder system. The piston has 50 g mass and a given radius of 3 cm. What amount of pressure does the piston exert? (Use g =9.8 m/s^2)
177 Pa
183 Pa
169 Pa
174 Pa
Question 14
Which of the following is an example of a open system?
A water bottle with a top on.
An unopened jar of peanut butter
An enclosed fish tank.
A cup of coffee
Question 15
You are replicating a lab and want to check your measurements (SI units) with a previous experiment’s measurements taken in English units. You found the density of water to be 980 kg/m^3, the volume of the water in a tank to be 53.1 cm^3 and the temperature of water to be 20 °C. If the numbers used in the previous experiment (completed in English units) were 1.93 slugs/ft^3, 5616 in^3, 68 °F, do you need to change any part of the experiment?
Everything needs to change. None of the numbers match up.
The volume of water in your experiment needs to be change. It is much smaller than that of the previous experiment!
The temperature of water needs to change. It is significantly higher than that of the previous experiment.
Nothing needs to change.
Answers
Q1.) All of the other choices are correct
Yes! Without the transfer of energy, none of these systems would be successful at what they were designed to do.
Q2.)High Energy Density Fuels
Jets are required to carry the fuel on-board, unlike power plants. Jets have to travel larger distances requiring more fuel mass than scooters. Fuel weight is small compared to the freight mass for locomotives.
Q3.) Energy demands will continue to increase with population over the next twenty years
As population increases, the demand for energy will also increase. Fossil fuels are limited, so we must find new options to keep energy supply where the demand will be in coming years
Q4.)159 cm^3 / s
Physically, this problem can be answered by knowing that the air is flowing at a given speed through a cross-sectional area that can be calculated using the given radius. This product of speed and area will result in the volume flow rate of the air. This can be checked by ensuring that the units being multiplied result in a unit for volume flow rate, which it does here.
Q5.) Heat is being transferred from the lightbulb to the lamp
Correct! Heat transfer occurs from the hotter object to the cooler object.
Q6.)Intensive Property
Color does not change if you increase or decrease the mass of the substance.
Q7.) 177 degrees Celsius
Q8.) A system is a closed system is the rate of mass into and out of the system is equal.
This is not true. If there is mass entering or leaving the system, the system is an open system. Heat and Work can cross the boundaries of a closed system but mass cannot.
Q9.) No
This is not steady state because the temperature of the room changes with time.
Q10.)4.4 m/s
You set the potential energy of the ball equal to the kinetic energy of the ball!
The Correct Answer and Explanation is :
Q1: Which of the following is an example of a system where the transfer of energy is important?
Answer: All of the other choices are correct.
Explanation: Each of the listed systems involves some form of energy transfer, whether it’s electrical, mechanical, or thermal energy. For example:
- The battery in your phone: Energy is transferred from the battery to power the phone.
- The air-conditioning unit: Energy is transferred to or from the room to cool it down.
- The computer: Electrical energy powers the computer, and heat energy may be transferred from the internal components.
- A convection oven: Heat is transferred through convection, enabling the oven to cook food.
Q2: The Jet Aircraft industry has the highest need for
Answer: High Energy Density Fuels
Explanation: Jet engines require fuels that contain a large amount of energy per unit mass because aircraft need to carry sufficient fuel for long-distance travel while minimizing weight. High energy density fuels, like aviation gasoline or jet fuel, provide the necessary energy in a compact form.
Q3: Why is it important to find new sources of energy?
Answer: Energy demands will continue to increase with population over the next twenty years.
Explanation: As the global population continues to grow, energy demands will rise. Traditional sources, such as fossil fuels, are limited and may become less economically viable over time. Therefore, finding new sources of energy is crucial for meeting future demands.
Q4: You need to fill a football with air to play with it. You know that your pump expels air at 8.2 ft/s. The needle of your pump has a radius of 4.5 millimeters. What is the volume flow rate of the air being pumped into the football?
Answer: 159 cm³ / s
Explanation: The volume flow rate can be calculated using the formula:
[
Q = A \times v
]
Where:
- ( Q ) is the volume flow rate.
- ( A ) is the cross-sectional area of the pump needle, calculated as ( \pi r^2 ).
- ( v ) is the velocity of the air (8.2 ft/s).
After calculating the area and multiplying by the velocity, we convert the units appropriately, which gives a volume flow rate of 159 cm³/s.
Q5: A lightbulb is sitting in a lamp. You notice that the lamp becomes warm. Which of the following is true?
Answer: Heat is being transferred from the lightbulb to the lamp.
Explanation: When a lightbulb is on, it produces heat. In this case, the lamp absorbs the heat from the lightbulb, causing it to warm up. Heat always transfers from the hotter object to the cooler one.
Q6: Color is an example of an
Answer: Intensive Property
Explanation: Intensive properties are independent of the amount of substance present. Color is one such property because it does not change whether you have a small amount or a large amount of a substance.
Q7: You need to set the oven to 450 Kelvin. What temperature do you need to set the oven to in Celsius?
Answer: 177 degrees Celsius
Explanation: To convert from Kelvin to Celsius, use the formula:
[
T_C = T_K – 273.15
]
Thus, ( 450 – 273.15 = 177 ) °C.
Q8: Which of the following is not true of a closed system?
Answer: A system is a closed system is the rate of mass into and out of the system is equal.
Explanation: This statement is incorrect because a closed system does not allow mass to enter or leave the system, but energy in the form of heat or work can still cross the boundaries.
Q9: If the temperature of a hot room with an open window is modeled by T(t) = 72 – 0.25(t), is this a steady-state condition?
Answer: No
Explanation: The temperature in this model decreases over time, indicating that the room is cooling down. A steady-state condition would imply that the temperature remains constant.
Q10: A ball, with a mass of 0.06 kg, falls off a table (assume it was on the edge and started with no velocity). If the table was 1 meter off the ground, what is the velocity of the ball when it hits the ground?
Answer: 4.4 m/s
Explanation: The velocity of the ball can be calculated using the principle of conservation of energy. The potential energy of the ball at the height of 1 meter is converted into kinetic energy as it falls. The equation for velocity is:
[
v = \sqrt{2gh}
]
Where:
- ( g = 9.8 \, \text{m/s}^2 ) is the acceleration due to gravity.
- ( h = 1 \, \text{meter} ) is the height from which the ball falls.
Solving this gives a final velocity of approximately 4.4 m/s.
Q11: Consider a jar of molasses. The empty jar weighs 20 grams and is 6 cm tall with a 3 cm diameter. A jar with molasses weighs 90 g. What is the density of the molasses?
Answer: 1.21 g/cm³
Explanation: First, calculate the volume of the jar using the formula for the volume of a cylinder:
[
V = \pi r^2 h
]
Where ( r ) is the radius of the jar (1.5 cm) and ( h ) is the height (6 cm). The mass of the molasses is 90 g – 20 g = 70 g. Then, the density is:
[
\rho = \frac{\text{mass}}{\text{volume}} = \frac{70 \, \text{g}}{V \, \text{cm}^3}
]
This calculation results in a density of 1.21 g/cm³.
Q12: If the gauge pressure is reported as 6 atm, what is the absolute pressure?
Answer: 8 atm
Explanation: Absolute pressure is the sum of atmospheric pressure and gauge pressure. If the gauge pressure is 6 atm, and atmospheric pressure is 1 atm, the absolute pressure is:
[
P_{\text{abs}} = P_{\text{gauge}} + P_{\text{atm}} = 6 \, \text{atm} + 2 \, \text{atm} = 8 \, \text{atm}
]
Q13: Consider a vertical piston/cylinder system. The piston has a 50 g mass and a given radius of 3 cm. What amount of pressure does the piston exert?
Answer: 174 Pa
Explanation: The pressure exerted by the piston is given by:
[
P = \frac{F}{A}
]
Where ( F = mg ) is the force due to the piston’s weight, and ( A = \pi r^2 ) is the area of the piston. After calculating, the pressure is 174 Pa.
Q14: Which of the following is an example of an open system?
Answer: A cup of coffee
Explanation: An open system allows both energy and matter to enter and leave. A cup of coffee is an open system because heat can be transferred from it, and matter (steam) can evaporate.
Q15: You are replicating a lab and want to check your measurements (SI units) with a previous experiment’s measurements taken in English units. You found the density of water to be 980 kg/m³, the volume of water in a tank to be 53.1 cm³, and the temperature of water to be 20 °C. If the numbers used in the previous experiment (completed in English units) were 1.93 slugs/ft³, 5616 in³, and 68 °F, do you need to change any part of the experiment?
Answer: Everything needs to change. None of the numbers match up.
Explanation: The units in the SI system (kg, m³, °C) do not directly match the units used in the English system (slugs, ft³, °F), so the experiment would need to adjust to ensure unit consistency.