Download Integrated Science Energy Test

Integrated Science
Energy Test
Name: ____Answer Key_______________
For multiple choice, please circle the correct letter. For short answer, be sure to use complete sentences and
lots of details. To get full credit, you must show your work on any problems that require calculations!
1. A 50-kg cheetah is running at 15 m/s. What is its kinetic energy? (2 pts)
½ mv2 = ½ (50 kg) (15 m/s)2 = 5,625 J
2. A diver with a mass of 70 kg stands motionless at the top of a 3-m-high diving platform. Calculate his
potential energy. (2 pts)
PE = mgh = (70 kg) (9.8 m/s2) (3 m) = 2,058 J
3. Can an object have both kinetic energy and potential energy at the same time? Explain. (2 pts)
Yes, a falling object will have both kinetic energy and potential energy until it hits the ground. As the object
falls, the potential energy is converted into kinetic energy.
4. An example of an object having elastic potential energy is: (1 pt)
a) A stretched spring
b) Books on a shelf
c) A moving arrow
d) A falling star
5. Energy stored in the bonds between atoms is called: (1 pt)
a) Kinetic energy
b) Mechanical energy
c) Chemical energy
d) Thermal energy
6. What is a source of nuclear energy that we are exposed to every day? (1 pt)
The sun is a source of nuclear energy that we are exposed to every day.
7. Name the four of the seven main types of electromagnetic waves: (4 pts)
The seven types of electromagnetic waves are gamma rays, x-rays, UV rays, visible light, infrared waves,
microwaves, and radio waves.
8. Look at the graphs below. One of the graphs is a plot of kinetic energy vs. mass for a set of objects with
different masses, all moving at the same speed. The other graph is a plot of kinetic energy vs. speed for a set
of objects with the same mass, all moving at different speeds. Identify each graph and explain how you can
tell which is which. (3 pts)
Graph 1
Graph 2
Graph 1 is a graph of kinetic energy vs. velocity. Graph 2 is a graph of kinetic energy vs. mass. I can tell
because kinetic energy to velocity is an exponential relationship, thus the graph is curved. Kinetic energy to
mass is a linear relationship, thus the graph is a straight line.
9. The law of conservation of energy states that: (1 pt)
a) Energy cannot be converted from one form to another
b) Energy cannot be created or destroyed
c) Energy resources must be used efficiently
d) Energy is constantly being lost to friction.
10. Describe how the energy changes form as it travels from the sun through green plant into the rabbit. (4 pts)
The sun converts nuclear energy to electromagnetic energy. The plant then converts the electromagnetic energy
into chemical energy via photosynthesis. The rabbit then eats the chemical energy from the plant and converts it
into mechanical energy via digestion.
11. Complete the following block diagrams: (2 pts)
Electromagnetic energy out: 9,000 J
Mechanical energy in: 10,000 J
Mechanical energy out: __1,000 J____
Mechanical energy out: 5,454 J
Thermal energy in: _14,714 J___
Thermal energy out: 9,260 J
12. Given the following diagram, what is the energy efficiency of an incandescent light bulb? (2 pts)
Electromagnetic energy in:
60 J
Light energy out: 1.5 J
Heat energy out: 58.5 J
Energy efficiency: ___1.5 J/60 J x 100% = 2.5%________________
13. Can energy conversions ever be 100% efficient? Why or why not? (2 pts)
No. Some energy is always converted to unusable waste heat due to friction.
14. In what direction does heat flow on its own spontaneously? (1 pt)
a) From north to south.
b) From hot to cold
c) From top to bottom of an object
d) From cold to hot
15. Which term describes the measure of the average kinetic energy of the particles in an object? (1 pt)
a) Potential energy
b) Thermal energy
c) Temperature
d) Specific heat
16. The best thermal insulators: (1 pt)
a) Conduct heat well.
b) Are metals.
c) Are gases.
d) Have free electrons.
17. A hot bowl of soup is sitting on a thick cloth pad. Heat from the soup is
transferred in several ways. List 2 ways in which heat is transferred away
from soup in this situation. (2 pts)
Heat is transferred away from the soup via convection in the form of steam.
Heat is also transferred away from the soup via conduction from the bowl to
the cloth pad. All objects radiate energy so heat is also transferred away from
the soup via radiation.
18. Why is conduction slower in gases than in solids? (1 pt)
The atoms in gases are further apart than in solids so they collide less often.
19. Explain how changes in a fluid’s density enables convection to occur: (2 pts)
As a liquid gets hot, the atoms collide more often and spread further apart. This causes the density to decrease
and the liquid to rise. Colder, denser fluid then takes its place. This creates a current.
20. Give one example of convection currents that occur in natural cycles. (1 pt)
One example of convection currents that occur in natural cycles are the weather patterns (especially wind),
ocean currents, and the movement of the Earth’s plates.
21. Why does tile feel cooler than carpet on your bare feet on a cold winter’s morning? (1 pt)
Tile is a better thermal conductor than carpet so it transfers the heat away from your feet.
22. An iron spoon and silver spoon have the same mass. Which becomes hotter when both are left in the same
cup of hot tea for one minute and why? The specific heat for iron is 0.449 J/(g•⁰C) and the specific heat for
silver is 0.235 J/(g•⁰C). (2 pts)
The silver spoon becomes hotter because it has a lower specific heat which means it takes less energy to raise its
temperature.
Material
Copper
Gold
Lead
Tin
Zinc
Specific Heat
[J/(kg•⁰C)]
385
449
129
228
388
23. According to the table above, a 2-kg block of which of the following materials would require 898 joules of
heat to increase its temperature by 1 ⁰C? (1 pt)
a) Gold
b) Lead
c) Tin
d) Zinc
24. A cup of coffee at 120 ⁰F is left in a room that is 72 ⁰F. How and why does the coffee come to thermal
equilibrium with the room? Use details! (4 pts)
In nature, all systems move to achieve thermal equilibrium by transferring heat energy from hot to cold. The hot
coffee in the cup conducts energy into the room by vibration of particles. The fast moving particles in the coffee
cause the particles in the cup to vibrate faster and heat up. This is turn causes the air molecules surrounding the
cup to vibrate faster and heat up. The coffee also convects heat through steam. Finally, it radiates heat into the
room. The heat change in the room cannot be felt because the mass of material in the room is so great compared
to the mass of material in the cup.
25. Look at the following graph showing the temperature of a bowl of soup and a glass of ice water left in the
same room. Based on the information presented, what is the temperature of the room? (1 pt)
Temperature (deg F)
Temperature of the room: ___~55 ⁰F_______
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Soup
Ice Water
0
5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Minutes
26. Work is the product of: (1 pt)
a) Speed and force
b) Power and force
c) Force and distance
d) Motion and force
27. Explain how the scientific definition of work is different from the everyday meaning. (2 pts)
The scientific definition of work is the force times the distance when the force is acting in the same direction as
the displacement. The everyday meaning can include everything from chopping wood, to lecturing students, to
raising children. The everyday meaning is much broader than the scientific meaning which is very precise.
28. In an ideal machine, which of the following is true? (1 pt)
a) Work input is equal to work output.
b) Work input is greater than work output.
c) Work input is less than work output.
d) The IMA is always equal to one.
29. Do ideal machines exist? Why or why not? (2 pts)
Ideal machines do not exist because some work is always lost due to friction.
30. A machine has an efficiency of 60%. What happens to 60% of the work put into the machine, and what
happens to the other 40%? (2 pts)
The other 40% is lost due to unusable waste heat caused by friction.
31. What is one good way to increase the efficiency of a machine? (1 pt)
One good way to increase the efficiency of a machine is to reduce its friction.
Important Equations:
KE = ½ mv2
PE = mgh
Challenge questions (Extra credit 1% each. You must show your work!)
1. An asteroid is hurtling toward Earth at a speed of 150 km/s. It is 25 m wide and has a density of 12 kg/m3. How much
kinetic energy will the asteroid have when it hits Earth? Assume that the asteroid is a perfect sphere, that none of the
asteroid burns up in Earth’s atmosphere, and that its speed does not decrease. V=
V=
= 1.33 (3.14) (12.5)3 = 8,181 m3
8,181 m3 (12 kg/m3) = 98,175 kg
v = 150 km/s x 1000m/km = 150,000 m/s
KE = ½ mv2 = ½ (98,175 kg) (150,000 m/s)2 = 1.10 x 1015 J
2. How much energy does it take to raise 500 g of gold, 7 degrees Celsius?
449 J
kg∙⁰C
0.5 kg 7 ⁰C
= 1,572 J
3. If a hydroelectric power plant is 87% efficient, the electricity distribution lines experience a 12% loss, and your
incandescent bulbs are 5% efficient, how much energy does the power plant need to produce to make 64 J of light?
You must complete a block diagram and show your calculations.
It takes 1672 J of energy to produce 64 J of light.
1672 J
Hydroelectric Plant
(87% efficient)
1455 J
64/0.05 = 1280/0.88 = 1455/0.87 = 1672 J
Electric Lines
(88% efficient)
1280 J
Incandescent Light
Bulb (5% efficient)
64 J