Title: Energy Conversion: Summary Questions

Energy Conversion Review Questions

Let's go over some of the big concepts in this chapter. Fill in the missing words.

Q: [...] is the process of transforming one form of energy into another. The science behind this is called [...].
A: Energy conversion/Conversion; thermodynamics
Q: The first law of thermodynamics can also be referred to as the [...] of energy principle. This means that energy is neither [...] nor [...] during a process.
A: conservation; destroyed/created/lost/wasted; destroyed/lost/wasted/created
Q: Temperature and pressure are examples of thermodynamic [...]. 2 independant properties define a thermodynamic [...].
A: properties; state
Q: Efficiency can be stated generally as the ratio between [...] to [...] of a system. It is an indicator of how much you get out for what you put in.
A: output; input

1st Law Analysis

Conservation of Energy

Q: A river is flowing at a constant velocity of 5m/s, and eventually flows into a lake at the bottom of a hill where there is a power generator unit. There is a 100m height difference.

If the volume flow rate is 500 cubic meters/s, how much power can be potentially generated? NOTE: Water density is 1000kg/m^3
- 490.50MW (correct)
- 491.75MW
- 496.75MW
- 6.25MW

HINT:

Q: Let's cook some rice in a pressure cooker.

Initially, the rice has an internal energy of 10kJ before cooking. During cooking, 50kJ of heat are added to the pot while 10kJ escapes to the environment. Additionally, the pressure cooker does 500N-m of work on the rice. What is the final internal energy content of the cooked rice? Hint: Pay attention to the units.
- 50.5 kJ (correct)
- 550 kJ
- 55.0kJ
- 49.5kJ

[Image: Pressure Cooker]

Q: Students complain that their classroom gets too hot on summer days and rally to get some air conditioning units installed.

A classroom contains an average of 30 students. Typically, a person emits 360kJ of heat per hour. Additionally, there are 10 lighting units in the room with ratings of 100W. The average heat transfer in through the walls of the class is estimated to be 14400kJ/h.

If each AC unit has a cooling capacity of 2kW, how many units are needed to maintain the base temperature of 21C?
- 4 units (correct)
- 3 units
- 2 units
- 5 units

HINT: Think about how you want to define the system, and what the inputs and outputs are to this system.

Thermodynamic properties

Thermodynamic Properties

Let's go over thermodynamic properties and their relation in internal energy of the system. Drag the words into the correct boxes.

Q: Consider a closed system with a certain number of gas particles moving inside.

An increase in [...] can be induced by increasing the gas [...] - this can be achieved by decreasing the [...] of the system.

An increase in [...], which is directly related to the internal energy, can be achieved by adding [...] to the system and raising its [...].
A: internal energy; pressure; volume; particle speed; heat; temperature

Q: On a sunny weekend, you decide to go camping in the Alps and decide to pitch your tent near the summit of the mountain.

After a good hike, you begin to prepare dinner of some boiled potatoes by heating some water over a fire. Do you expect your dinner to cook faster or slower at this altitude?
- It will cook slower than normal (correct)
- It will cook faster than normal
- It will take the same amount of time

Hint: Think about the pressure at this altitude. Is it higher or lower than normal?

Efficiencies

Q: An electric motor has an operating efficiency of 80%. If the input to the motor is 300kW, how much would you expect the power output to be?
- 240kW (correct)
- 375kW
- 320kW
- 225 kW

NASA's Mars Curiosity Rover is powered by a radioisotope power system, that takes heat from the radioactive decay and converts it to electric energy.

NASA Rover example

Fill in the blanks for this energy conversion process.

Q: The final energy in this case would be [...]. Before this, the secondary energy is in the form of [...]. This comes from the radioactive decay serving as an energy conversion process, with the primary energy source being [...].
A: electricity; heat; plutonium

https://mars.nasa.gov/msl/spacecraft/rover/summary/

NASA's Mars Curiosity Rover is powered by a radioisotope power system, that takes heat from the radioactive decay and converts it to electric energy.

Q: Given that the power density of Plutonium is 540W/kg, calculate the electrical power that a 1kg sphere of Plutonium can generate given an efficiency of 17%.
- 91.8W (correct)
- 3176.5W
- 523.0W
- 100.0W

https://mars.nasa.gov/msl/spacecraft/rover/summary/