Physical Science 103
Fall, 2016
Exam #2 Review
OBJECTIVES
Work, Power& Energy
 Calculate the work required to lift an object a specific height.
 Calculate the gravitational potential energy of an object at a given height.
 Calculate the velocity & kinetic energy of a falling object.
 Calculate the power required to perform an activity.
 Identify the energy transformations that occur in a device, such as a light bulb.
 Convert between the units joules, calories, and Calories.
Heat and Heat Transfer
 Compare the properties of substances with high and low specific heat capacities.
• Conduct an experiment to explain how specific heat capacity influences the change in
temperature of a substance.
 Compare the mathematical proportionality of mass, temperature change, specific heat, and heat.
 Conduct an experiment to determine the specific heat of an unknown substance.
 Explain temperature in terms of the kinetic energy of the particles of a substance.
 Explain how energy is transferred via conduction, convection and radiation.
 Explain the effect of temperature on the volume, pressure, and density of a substance.
 Explain why the color black is a better absorber of radiant energy than white.
 Explain the effect of temperature on the pressure exerted by a gas.
 Distinguish between a thermal conductor and an insulator.
Electricity
 Describe the motion of electrons from negative towards the positive terminal when using a battery.
 Recognize and apply the concepts of current, voltage and resistance in a series and parallel circuit.
 Using Ohm’s Law and the equation for electrical power, apply and calculate for each of the variables and
use their units appropriately.
 Identify basic electrical components (battery, wire, bulbs) in terms of schematic diagrams. Draw and
interpret schematic diagrams of simple and compound circuits.
 Combine cells in parallel and in series and know how these combinations affect voltage in a circuit.
 Combine light bulbs in series and in parallel and be able to predict how these combinations affect the
current and voltage in the circuit.
 Predict how undoing a light bulb in a parallel or series circuit affects the current, voltage, and resistance in
the other parts of the circuit.
 Differentiate between D.C. and A.C. current.
 Show that kilowatt-hour is a unit of energy and be able to calculate the number of kilowatt-hours used by
an electrical device and its cost if one knows its voltage, current, time of use and the cost per kilowatt-hr.
1. Using the car, ramp, meterstick, stopwatch, and balance:
a.
Calculate the potential energy of the car at the top of the ramp.
b.
Determine the final velocity of the car at the bottom of the ramp.
c.
Determine the kinetic energy of the car at the bottom of the ramp.
d.
The average acceleration of the car down the ramp.
e.
The force required to accelerate the car down the ramp.
f.
The amount of energy "lost".
g.
Account for the "lost" energy, how do you account for it being "lost"?
h.
The efficiency of the car in converting potential energy into kinetic energy.
Data Table
Mass of car: 50.00 g
Time (Trial 1) 2.30 s
Height of Ramp: 20.00 cm
Length of Ramp: 180.0 cm
(Trial 2) 2.45 s
(Trial 3) 2.40 s
2. A child on a swing set has a mass of 40.0 kg (approximately 100 lbs). At the top of the swing the child is
2.00 meters above the low point of the swing. How fast is the child moving at the bottom of the swing?
3. Give an example for the following energy transformations:
Electrical to radiant
Chemical to mechanical
electrical to mechanical
4. My office in Clarke Science has no heat during some parts of the day during the winter. If you were to sit in
one of my chairs in the office you would notice that the steel legs of the chair feels much colder than the plastic
seat. Explain.
5. The specific heat capacity for water is 4180 J/kg oC. My coffee cup holds 300. mL of tap water which has
a temperature of 30.0 oC as it comes out of the tap. How many Calories of heat energy would be required to
make a boiling cup of coffee? 21 Calories
6. Why does a bimetallic strip made of copper and iron bends toward the copper strip when heated?
7.
A 85.00 gram sample of lead is heated in boiling water. After 10 minutes the lead is placed in a
Styrofoam cup with 100.0 mL of water at 20.0 oC. The final temperature of the water and lead at thermal
equilibrium is 23.0 oC. What is the specific heat of lead? (Specific heat of water = 4190 J/kg oC) 192 J/kg oC
5. Here is twist on a familiar problem. In order to determine the height of a building, a student drops a
1.50 kg mass of iron off the top floor of a very tall building. The temperature of the iron block was 22.5 oC
before it was dropped and it had a temperature of 24.0 oC after it hit the ground. What is the
height of the building? (Specific heat of iron = 450 J/kg oC)
68.9 m
6. Aluminum has a larger specific heat capacity than copper. If equal masses of aluminum and copper wire are
placed boiling water and then allowed to cool on the table, will one metal undergo a faster decrease in
temperature, or will both cool at the same rate? Explain your answer.
7. The specific heat of granite is 890 J/kg oC. You start the experiment by placing a piece of granite into a hot
oven set at 450 oF (230 oC). After heating for 15 minutes, you place the granite into a Styrofoam cup containing
100.0 mL of water at 20.0 oC. The temperature of the water rises to 32.0 oC. What was the mass of the piece of
granite that was heated in the oven? 28.5 g (0.0285 kg)
8. Two equal masses of aluminum and copper are dropped from a very tall building and allowed to impact the
ground. Aluminum has a specific heat capacity three times that of copper. Compare the two metals for the
following:
a. The GPE when released.
b. The KE at the point of impact.
c. The temperature after impact.
9. The nutrition label on a package of processed cheese food indicates that a 20.0 g serving has 175 Calories.
To test this you put a small piece of cheese under a can with 100.0 mL of water and burn the cheese. You find
that 1.0 gram of cheese was burned to heat the water. Assume that all of the heat released by the cheese was
absorbed by the water (let’s pretend), what is the change in temperature of the water at the end of the
experiment? 87.5 oC
10. A student takes a 1.0 kg bag of lead to the top of the Empire State Building and drops it. The roof of the
Empire State Building is 380 meters above the street. The specific heat of lead is 190 J/kg oC. What is the
temperature change of the lead assuming that all of the gravitational potential energy is converted to heat?
19.6 oC
If the student repeated the experiment with a 1.0 kg bag of aluminum, which has a specific heat greater than
lead, how would this affect the outcome of the experiment?
11. What is the advantage of connecting batteries in series? Parallel?
12. A flashlight contains 4 D-cell batteries connected in series. What is the overall voltage for the flashlight?
13. Compare the voltage, resistance, current and cost of operating a 60 W light bulb and a 100 W light bulb.
14. Describe the properties of voltage, current and resistance in a series and parallel circuit.
Voltage
Current
Resistance
Series
Parallel
15. Every electrical appliance sold in America has 120 VAC / 60 Hz embossed somewhere on the case of the
appliance. What do these numbers represent?
16. Use the circuit diagram below to complete the table. Assume the resistance of the bulbs is
15 Ohms. The voltage of the battery is 14.0 V.
Bulb
Voltage
A
4.00 V
Current
B
A
0.13 A
14.0 V
C
B
C
D
E
E
D
a. What is the total resistance in the circuit as measured at the battery? 52.5 Ohms
b. What is the total current in the circuit as measured at the battery? 0.26 Amperes
c. In the above circuit, which bulb(s) is/are the brightest?
d. In the above circuit, which bulb(s) is/are the dimmest?
e. What would happen to bulb A if bulb D were unscrewed?
f. What is the voltage in all of the bulbs if bulb C were unscrewed? 3.5 V
17. Complete the table below. Assume National Grid charges $0.25 / kWh and the appliances are run for
10 hours each day during the month of August.
Appliance
Air Conditioner
Light bulb
Power
Voltage
Current
Resistance
1500 W
600 Ohms
Cost