Equation Sheet for Physics 103 Midterm 2 Efficiency = Useful Energy Out Total Energy In Efficiency Work Eff = Work out in W = F G M1 M2 F = 2 E pot = M g h F = M a F = M g E kin = _ M v 2 Actual Mechanical Advantage = F out F in s = t Theoretical Mechanical Advantage = in out a = v f v i t I = Q t F = k Q 1 2 Q 2 V = I R E = Q = C V 1 Q 2 cap V final P = E = W t t E pot = Q V P = I V R = ρ L A G = 6.67 x 10 11 N m 2 /kg 2 1 mile = 5,280 feet = 1.609 kilometers 1 lb = 4.45 N 1 joule = 0.74 foot pounds 1 kilowatt = 1,000 watts g = 9.8 m/s 2 = 32 ft/s 2 1 foot = 0.305 meters 1 hour = 3600 seconds 1 horsepower = 746 watts k = 8.99 x 10 9 N m 2 /coulomb 2 92
Sample Midterm 2A 1. A machine requires 200 joules of energy to raise a 50 N box 3 meters. What is the efficiency of the machine? a) 50% b) 67% c) 75% d) 82% e) 87% 2 The reason that a 15 watt fluorescent light bulb can give off about the same amount of light as a 60 watt incandescent light bulb is because a) the 15 watt fluorescent light bulb is more powerful than the 60 watt incandescent light bulb. b) the 60 watt incandescent bulb is more efficient in light production than the 15 watt fluorescent bulb. c) the 15 watt fluorescent light bulb is more efficient in heat production than the 60 watt incandescent light bulb. d) in addition to light, the 60 watt incandescent light bulb produces much more heat than the 15 watt fluorescent light bulb. e) the fluorescent bulb is larger than the incandescent bulb. 3. Samantha's complex machine is made up of a hydraulic jack with an efficiency of 50%, a lever with an efficiency of 60%, and a block and tackle with an efficiency of 40%. What is the overall efficiency of her machine? a) 12% b) 40% c) 60% d) 120% e) 150% 4. A 100 ohm resistor is attached to a 200 volt battery. How much charge flows through it in 3 seconds? a) 2 coulombs b) 6 coulombs c) 20 coulombs d) 80 coulombs e) 2000 coulombs 100
5. According to the video Edison's Miracle of Light, which of the following statements is TRUE? a) Edison advocated using alternating current (AC) instead of direct current (C), because transformers could easily change the voltage of alternating current. b) Lamp black (carbon) was used to make the first successful filament for an electric light bulb. c) Edison's direct current utilities were only efficient when the generating plant was far from the electric consumer's home or business. d) Edison developed the first light source that used electricity. e) Choices (b) and (c) are both true. 6. A charged styrofoam ring weighing 0.01 newtons is levitated with a charged rod. What is the electrical force supporting the ring? a) 0.001 newtons b) 0.01 newtons c) 0.098 newtons d) 1.0 newton e) 9.8 newtons 7. Brad weighs 200 pounds and climbs a 10 foot staircase in 5 seconds. Jennifer weighs 100 pounds and climbs a 16 foot staircase in 4 seconds. Which of the following is TRUE concerning the power expended or work done by each against the force of gravity? a) Brad produced more power. b) Jennifer produced more power. c) They produced the same amount of power. d) They did the same amount of work. e) Jennifer did more work. 8. Sandra has stored 6 coulombs of charge in a capacitor, and finds that the capacitor has a potential difference between the terminals of 24 volts. If she now reduces the charge stored on the capacitor to 3 coulombs, what will be the voltage across the terminals of the capacitor? a) 6 volts b) 8 volts c) 9 volts d) 12 volts e) 24 volts 101
9. Jason is using a block and tackle to lift a cement block to a height of 2 meters. He has to expend 140 joules to overcome friction plus 210 joules to work against the force of gravity. What must be Jason's power output if he is to lift the block the 2 meter height in 7 seconds? a) 50 watts b) 70 watts c) 100 watts d) 350 watts e) 700 watts 10. Which of the following demonstrates that like charges repel one another? a) a long wooden board spins when a charged rod is held near it b) a balloon sticks to a wall after the balloon has been rubbed on your hair c) a pith ball moves toward a charged rod d) a styrofoam ring floats above a charged rod e) static cling in clothes removed from a dryer 11. You plan to lift a 1000 pound box 10 feet vertically, using a block and tackle. If you assume that the block and tackle has no frictional loss and that you pull down on the rope with a force of 100 pounds, how much rope will you pull through the pulley? a) 50 feet b) 100 feet c) 150 feet d) 200 feet e) 250 feet 12. In class, a coil of wire was dropped into a container of liquid nitrogen. What happened to the wire? a) The resistance of the wire increased. b) The current through the wire increased. c) The current through the wire decreased. d) The magnetic field around the wire decreased. e) None of the above is a correct statement about what happened. 102
13. Listed below are several statements about capacitors. Which of the statements is/are correct? (REA ALL THE ANSWERS!) a) The capacitors used in class stored less energy than the batteries. b) A capacitor is analogous to a pump. c) Capacitor storage of energy is often used when you need a modest amount of electrical energy delivered in a very short time (high power). d) Answers a) and b) are correct statements. e) Answers a) and c) are correct statements. 14. Which of the following would contain the largest amount of energy? a) a soda can with an excess of positive charge b) a charged Leyden jar c) a 1 farad capacitor charged using 3 volt batteries d) a C cell battery e) a soda can full of gasoline 15. According to the video The Hidden City, which of the following is the LEAST expensive source of electricity for New York City? a) hydroelectric b) natural gas c) coal d) oil e) nuclear 16. The diagrams below show 1.5 volt batteries connected in a variety of ways. Which diagram shows a combination that gives 4.5 volts when voltage is measured across all of the batteries? a) b) c) d) e) 103
17. Your electric dryer requires 2000 watts to operate properly. If the voltage to the dryer is 220 volts, how much current does the dryer need to operate properly? a) 0.11 amps b) 9.1 amps c) 18.18 amps d) 4.4 x 10 5 amps e) The capacitance of the dryer is not given, so the current cannot be calculated. 18. A 50 watt bulb is connected to a 100 volt battery. What is the current passing through the bulb and what is the resistance of the bulb? a) 0.5 amps and 100 ohms b) 0.5 amps and 200 ohms c) 1 amp and 50 ohms d) 2 amps and 2 ohms e) 4 amps and 2 ohms 19. In class you gave a plastic rod a negative charge by rubbing it with a foam pad. You then brought the charged rod near a pivoting wooden dowel that had no net charge. Which of the following statements is TRUE? a) The wooden dowel was repelled by the charged plastic rod because the atoms in the wood were slightly deformed by the charge on the plastic rod. b) The wooden dowel was repelled by the charged plastic rod because many electrons in the wood moved to the end of the dowel that was farthest from the plastic rod. c) The wooden dowel did not move because it had no net charge. d) The wooden dowel was attracted by the charged plastic rod because many electrons in the wood moved to the end of the dowel that was farthest from the plastic rod. e) The wooden dowel was attracted by the charged plastic rod because the atoms in the wood were slightly deformed by the charge on the plastic rod. 20. When a current of 60 amps flows through a wire, the voltage drop across the wire is 1 volt. What is the resistance of the wire? a) 0.0083 ohms b) 0.0167 ohms c) 2 ohms d) 30 ohms e) 120 ohms 104
21. Which of the following simple machines can operate with an efficiency greater than 100%? a) a lever b) a block and tackle c) an inclined plane d) a winch e) None of these machines can operate with an efficiency greater than 100%. 22. One does not usually observe an electrostatic force between ordinary objects because a) objects are normally uncharged. b) there is no closed circuit between the objects. c) charge is conserved. d) electrostatic forces only act between objects that are very close together. e) the gravitational force between objects is much stronger. 23. An energy efficient electric stove costs $600 to buy and $75 per year to operate. A less efficient stove costs $450 to buy and $125 per year to operate. After 5 years, which stove has cost you more? a) The energy efficient model costs $100 more. b) The energy efficient model costs $100 less. c) The energy efficient model costs $300 less. d) The energy efficient model costs $400 less. e) The energy efficient model costs $675 less. 24. Wire A and wire B are both made of the same metal and are the same length. However, wire A has twice the cross-sectional area of wire B. Which of the following statements is TRUE? a) The resistance of wire A is four times the resistance of wire B. b) The resistance of wire A is two times the resistance of wire B. c) The resistance of wire A equals the resistance of wire B. d) The resistance of wire A is 1/2 the resistance of wire B. e) The resistance of wire A is 1/4 the resistance of wire B. 105
25. In class we tested the power requirements of a hand drill when a frictional load was applied. The power requirement of the drill operating with a load is its power requirement operating without a load. a) equal to b) greater than c) the same as d) _ as much e) _ as much 26. A circuit has three batteries and two light bulbs connected in series. The batteries each have values of 1.5 volts (none of them are reversed). If the voltage drop across one of the light bulbs is 3.0 volts, what is the voltage drop across the other bulb? a) 0.5 volts b) 1.0 volt c) 1.5 volts d) 3.0 volts e) Not enough information is given to answer this question. 27. Your electric power company charged you $70 for the 1000 kilowatt-hours of electrical energy you used last month. If you used your 1000 watt range for a total of 20 hours, how much did it cost you to operate the range? a) $ 0.07 b) $ 0.70 c) $ 1.40 d) $ 2.80 e) $ 3.50 28. A 0.8 farad capacitor is attached to a battery so that it is charged to a final voltage of 1.5 volts. How much charge is stored in the capacitor? a) 0.53 coulombs b) 1.2 coulombs c) 1.9 coulombs d) 1.9 joules e) 1.9 amperes 106
29. You have two balls, each with a mass of 1.0 kilogram. One ball has a charge of 1.0 coulomb and the other a charge of -1.0 coulomb. When the distance between the centers of the balls is doubled, what happens to the electrostatic force between them? a) The electrostatic force increases by a factor of two. b) The electrostatic force increases by a factor of four. c) The electrostatic force decreases by a factor of two. d) The electrostatic force decreases by a factor of four. e) The electrostatic force is unchanged. 30. You have just rubbed a plastic rod with foam. You bring the rod near a small neutral ball, but you O NOT allow the ball and rod to touch. What happens? a) The ball does not move. b) The ball is attracted to the rod. c) The ball is repelled by the rod. d) The ball will start spinning rapidly. e) None of the above happens. 107