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SPH 4C
Energy Transformations
Review
1.
What is work? What is energy? What is the formula for calculating work? What are
the units for work and energy?
2.
Name 6 different types of energy and an example of a source of that energy.
Ex. Sound (source = speaker)
3.
An engineer uses a single car to test the roller coaster track,
shown in Fig. B. In answering the following questions, assume
that friction can be ignored and the speed at A is O. In each
case, give a reason for your answer.
(a) Where is the gravitational potential energy the greatest?
(b) Where is the kinetic energy the greatest?
(c) Where is the speed the greatest?
(d) Give a written description of what happens to the speed of
the car as it rolls from A to B and so on to E.
Fig. B
4.
A 30 kg box is held 5.0 m above the ground. How much gravitational potential energy
does it possess? If it is lowered to 2.0 m above the ground, how much Eg was lost?
(1470 J; 882 J)
5.
A 0.025 kg bullet traveling at 245 m/s hits a tree. How much kinetic energy does the
bullet impart on the tree?
(750 J)
6.
What does the law of Conservation of Energy have to say about a falling rock?
7.
Why is energy never truly conserved in a mechanical system?
8.
Dr. Boom sends his 3.5 kg monkey straight up with a velocity of 24.0 m/s. How high
will the monkey go before it comes to a complete stop? (29.4 m)
9.
A 40 g spring with a constant of 24 N/m is stretched by 30 cm. If it is let go, and no
energy is lost, how high will the spring go? (2.76 m)
10.
A ball of mass 2 kg has a starting velocity of 7.0 m/s at the bottom of a ramp. It only
reaches a height of 2.0 m.
a) Calculate the total energy of the ball at the bottom of the ramp.
(49 J)
b) Calculate the gravitational potential energy of the ball at the top of the ramp.
(39.2 J)
c) How much energy did the ball lose?
(9.8 J)
d) Where did lost the energy go? (friction = heat, sound)
e) Calculate the efficiency of the ramp.
(80%)
\sph4C\energy\840982107
11.
Write the energy transformation equation (diagram) for using a slingshot.
12.
Explain why it is impossible to have a motor that is 100% efficient.
13.
When thermal energy is transferred, when does it stop?
14.
Why is the inside of an astronaut’s suit made from highly reflective material? From
what form of heat transfer is this protecting the astronaut?
15.
Describe each of the thermal energy transfer methods and give an example.
16.
Give examples of thermal energy loss in the home, and the type of transfer they are
(ie. conduction, convection, radiation).
17.
How can we protect against heat loss (give 3 examples)? Which type of transfer does
each insulation method prevent?
18.
A thermos is a good device for maintaining a liquid’s temperature. What methods of
insulation does it use?
19.
Sketch an energy flow diagram illustrating the efficiency of a car engine if 100% is
input from fuel, 5% is lost to air as sound, 4% is lost to the road as heat, and 70% is
lost from the engine as heat.
20. Sketch an energy flow / path diagram for a propane barbecue.
21.
If the average cost of electricity during mid-peak time of use is $0.089/kWh, how
much does it cost to run a 60 W lightbulb for 3 hours a night for a week? ($0.112)
22. Which are the most efficient types of light bulb in the home today? Which are the
least efficient?
23. a) Where is most of your electricity used in the home?
b) How can you as an individual reduce how much energy you use / waste in your
home?
24. In energy conservation, no energy is actually “lost”. Where, then, does the lost
energy go?
25. The specific heat capacity of water is 4200 J/(kgC). The specific heat capacity of
aluminum is 900 J/(kgC). If 2 kg of each substance had its temperature raised by
20 C, how much energy would be needed in total? (2.04 x 105 J)
\sph4C\energy\840982107