Sample Test 4 - Work and Energy
Some multiple choice questions may have more than one right answer. Indicate all correct choices. Correct incorrect statements.
1. Which of the following are correct statements?
a) Work is proportional to force and speed.
b) All forces on moving objects do work.
c) Work transfers energy from one type to another.
d) No force can do work on an object if it does not move.
e) Work is proportional to force and distance.
2. You push a physics book across a table. The book weighs 9 N, you push with a steady horizontal 6 N force, and the force of friction against the book is 2 N. You push the book a distance of 2 m. The amount of
work you do on the book is
work done by gravity is
work done by friction is
total work done on book
3. Which of the following is (are) example(s) of chemical energies? Circle correct examples. For those not selected, indicate what type of energy is indicated.
a) energy stored in gasoline
b) energy stored in a spring
c) energy stored in your body
d) energy in firewood
e) energy in the water in a cloud
4. Which of the following is a (are) correct statement(s). Circle correct statements. Correct incorrect statements.
a) In a collision, momentum is always conserved
b) The kinetic energy before a collision always equals the kinetic energy after the collision
c) An engine makes heat flow from a colder body to a hotter body
d) Efficiency of an engine is Output Work divided by Input Energy
e) Exhaust Energy + Work Done must equal Input Energy in an engine
5. An engine has an efficiency of 16%. If it does 4800 J of work, calculate the input energy and the exhaust energy.
If the temperature of the heat source is 500 K and the heat is exhausted at a temperature of 300 K, what is the maximum possible efficiency of the process?
| 6. Shown in the diagram is a Pressure-Temperature diagram for Water. Line AB is drawn at the sealevel pressure where water freezes at 0° C and boils at 100°C. Line CD is drawn at a lower pressure such as would be encountered at higher levels such as Denver. What does the graph indicate will happen to the freezing and boiling temperatures of water in Denver? | |
7. Answer the following:
a) A 12,000 Watt oven is used to cook a roast at 350°C for 3 hours. How many Joules of energy have been used in this process.
b) How much work is done by a 100 kg person while climbing up a set of stairs which take him up 12 meters. If the work is done in 20 seconds, what is the power being exerted?
8. Your left hand lifts a 3 N apple by 1.2 m and your right hand lifts a 4 N grapefruit by 0.8 m.
a) Which hand exerted the greater force? How much?
b) Which hand did more work? How much?
c) If the left hand accomplished the lifting in 0.6 seconds and the right hand accomplished the lifting in 0.4 seconds, which hand exerted the greater power? How much?
9. You throw two balls out of a window with the same speed. One is thrown horizontally and one is thrown straight down. Which one is traveling faster when it hits the ground? Use and explain the energy conservation principle. Ignore air friction. Answer is simple.
10. Answer each of the following:
a) In the United States, solar energy strikes the ground at an average rate of 200 watts / m2. At what average rate does solar energy strike a whole football field (about 100 m by 30 m)?
b) Recently annual U.S. population growth was 0.8 %. How long will it take for the population of the U.S. to double at this rate?