Physics Chapter 13  Work & Energy  Quiz Questions (#1 #8)

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Q11: Define the word “WORK. 
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A11: Work is the transfer of energy to an object by the application of a force that causes the object to move in the direction of the force. 
Q12: Are you doing “work” when an object is not moving? 
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A12: No, because the object did not move. If you move 8 Newtons 0 meters, then using the formula W = F * D, 
Q13: What is the formula to determine work? 
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A13: The formula to determine work is W = F * D (Work = Force * Distance) 
Q14: In the formula for work, what unit of measurement is used for FORCE? 
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A14: The unit of measurement for FORCE is Newtons (N). 
Q15: What is the SI unit for work? 
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A15: The SI unit for work is Joules (J). 
Q16: One Newton lifted one meter = how many units of work? 
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A16: 1N * 1m = 1J One Newton lifted one meter = 1 unit of work (Joules) 
Q17: If you are given the mass of an object and the distance it is moved, what would the resulting formula for work be? 
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A17: This one is tricky. If given the mass of the object and the planet on which it occurs, you can derive Force ( F = m * a). So the resulting new formula for work is.... W = m * g * d (Work = mass * gravity * distance) 
Q18: You are standing in the gym holding a set of barbells above your head. Are you doing any work? 
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A18: No. Since you have not moved the barbells, you have done no work. W = F * D. Let's suppose the barbells have a mass of 100 kg., then W = 100kg * 9.8 m/s/s * 0 m (Work = 0 joules) 
Q19: Three children are struggling to move a large rock, After much effort, they manage to move the rock one centimeter. Have they done any work? 
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A19: YES! No matter how much they struggle, no matter how much "effort" they put into the job, if they don't move the rock, they have done NO WORK. But, in this example, since they moved the rock, they have done work! 
Q110: A machine takes 50 units of work to lift an 8 Newton rock 5 meters. How many units of work are expended as heat? 
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A110: Using the formula W = F * D (Work = Force * Distance) we can first calculate how much work the machine did to lift the rock. 8N * 5meters = 40 joules. Now we SUBTRACT the 40 J from the 50 J the machine is putting out and we come up with 10J of energy lost to heat. 
Q21: Define the word “POWER.” 
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A21: Power is a quantity that measures the rate at which work is done or energy is transformed. 
Q22: Give the formula for power. 
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A22: The formula for Power is... Power = Work / Time P = W / T 
Q23: Power is measured in what unit? 
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A23: Power is measured in "watts." 
Q24: One unit of power is the amount needed to do ……. 
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A24: One unit of power is the amount needed to do one Joule of Work in one second. 
Q25: What is the formula for POWER if a word problem includes FORCE, DISTANCE, and TIME? 
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A25: Since the formula for power is P = W/T you need to modify the "W" to include Force * Distance. Therefore the new formula would be P = F * D / T 
Q26: What is the unit of measurement for WORK? 
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A26: The unit of measurement for WORK is Joules 
Q27: Would your power output increase or decrease if you walked up a set of stairs faster? 
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A27: If you decrease the time in which the job is done, you have INCREASED your power output. 
Q28: Would your power output increase or decrease if you carried a set of books weighing 20 Newtons up the stairs in the same amount of time as without the books? 
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A28: If you increase the force (by adding mass in the form of books) and do the job in the same amount of time, you have increased your power output. 
Q29: While rowing across a lake during a race, John does 3960 Joules of work on the oars in 60 seconds. What is his power output? 
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A29: P=? W=3960J T= 60s Power = W / T Power = 3960 J / 60 seconds Power = 66 watts 
Q31: Define mechanical advantage. 
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A31: Mechanical advantage is a quantity that expresses how much a machine multiplies force or distance 
Q32: Can an inclined plane have a mechanical advantage of less than one? Why or why not? 
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A32: Or, if you asked this question: What is the smallest mechanical advantage possible with an inclined plane? The answer is one (1). Here is why: If you lift an object straight up and the object weighs 500 grams, you have expended 500 grams of force to lift the object. 500 / 500 = 1. So, lifting an object straight up yields a mechanical advantage of 1. Therefore, an inclined plane, even if it is a vertical slope, will never have an MA of less than one. 
Q33: What is the mechanical advantage of a single fixed pulley? 
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A33: One (1) A single fixed pulley really doesn't help you any. The down strand is just changing the direction of the force, so it's mechanical advantage is only one (1). 
Q34: What is the mechanical advantage of a pulley system with 4 supporting strands? 
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A34: Four (4) 
Q35: What is the mechanical advantage of a single MOVEABLE pulley? 
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A35: Two (2) 
Q36: In many of our labs we used a Force Produced and Force Applied to derive Mechanical Advantage. What is the formula? 
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A36: MA = FP / FA 
Q37: Is it any advantage to use a machine that has a mechanical advantage of less than one? 
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A37: In our lab on levers, we did get mechanical advantages of less than one. In those cases, you are expending more force to lift the object than if you just went over and picked the object up. So, having a mechanical advantage of less than one would be a huge waste of time and energy. 
Q38: A ramp at ANY ANGLE must have a mechanical advantage greater than what? 
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A38: One (1) 
Q39: You have access to a short, steep ramp and a long, gradual ramp. Obviously, they require different amounts of effort to move a heavy object up each ramp. Compare the WORK done by the two ramp systems. 
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A39: Remember that WORK is defined as FORCE * DISTANCE. So, even though with a long, gradual ramp you are using less effort, ultimately you reach the same height (distance above starting place) as when you use the short, steep ramp. Also, the short ramp has less distance, but more force is required and the longer ramp has more distance but less force is required. So the answer to this question is that you are using the SAME AMOUNT OF WORK on both ramps. 
Q310: In our levers lab it was suggested that it is possible to lift a car with your little finger. Explain the lever system that would make this possible. 
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A310: 
Q41: List the 6 simple machines. 
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A41: Six Simple Machines: lever, pulley, wheel & axle, inclined plane, screw, wedge 
Q42: Give an example of a first class lever. 
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A42: First Class Lever examples: 
Q43: Give an example of a second class lever. 
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A43: Second Class Lever examples: 
Q44: Give an example of a third class lever. 
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A44: Third Class Lever examples: 
Q45: What is the mechanical advantage of a single fixed pulley? 
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A45: One (1) 
Q46: What is the mechanical advantage of a pulley system with 3 supporting strands? 
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A46: Three (3) 
Q47: What is a COMPOUND MACHINE? 
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A47: A compound machine is made up of two or more simple machines. 
Q48: Name three compound machines. 
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A48: Examples of compound machines: 
Q49: How does an inclined plane change the force required to do work? 
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A49: The inclined plane increases the DISTANCE over which the force is applied. 
Q410: How does a pulley system change the force required to do work? 
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A410: A pulley system increases the DISTANCE over which the force is applied. Remember that each time we increased the number of supporting strands, you had to pull the strand down further. Lift distance decreased and "pull distance" increased. 
Q411: Does a single fixed pulley do the same amount of work as a double fixed and double moveable system with 4 supporting strands? 
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A411: Yes. Work = Force applied (in Newtons) * Distance moved. 
Q51: Define energy. 
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A51: Energy is the capacity to do work 
Q52: Define potential energy. 
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A52: Potential energy is the energy that an object has because of its position or configuration. 
Q53: Define kinetic energy. 
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A53: Kinetic energy is the energy of an object due to the object's motion. 
Q54: What is the formula for determining potential energy? 
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A54: PE = m * g * h 
Q55: What is the formula for determining kinetic energy? 
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A55: KE = 1/2mv^{2} 
Q56: Using PE for potential energy, and KE for kinetic energy, list the PE and KE for a roller coaster car at the top of its first hill and then at the bottom of the hill. 
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A56: Top of Hill: PE = high; KE = low 
Q57: What type of energy is found in a match before it is struck? 
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A57: The type of energy found in a match before it is lit is ....... 
Q58: Define mechanical energy. 
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A58: Mechanical energy is the amount of work an object can do because of the object's kinetic and potential energies. 
Q59: What organism is able to turn light energy into chemical energy? 
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A59: The organisms that can turn light energy into chemical energy are: PLANTS 
Q510: Explain the energy transformation when wood is burned. 
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A510: Stored chemical energy is released as HEAT and LIGHT 
Q511: Water storage tanks are usually built on towers or hilltops. Why? 
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A511: Water storage tanks are built on towers or placed on hilltops in order to build up a lot of Potential Energy. When the water comes down from the tower that potential energy is transformed into Kinetic energy and so the water thoughout the town will have enough water pressure to go through pipes into houses & businesses. 
Q61: Define the Law of Conservation of Energy. 
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A61: The Law of Conservation of Energy is that  
Q62: If the Law of Conservation of Energy is true, how could a girl’s second bounce on a trampoline be higher than her first? 
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A62: Given the same push, this is not possible. The only way she could bounce higher the second time is if she put more energy (force) into her jump. 
Q63: A tennis ball is allowed to bounce on a table top. Each bounce is lower and lower. Why aren’t all the bounces the same height? 
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A63: A tennis ball bounces lower each time because it looses energy due to friction, air resistance, heat, and momentum absorption by the table surface. 
Q64: Describe the energy changes as a car goes from the top of a roller coaster hill to the bottom. 
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A64: Top: Lots of PE, very little KE 
Q65: You have a coat hanger in your hand. You bend it back and forth 10 times and then feel the bent area. It feels hot to the touch. Describe the energy transformation that has occurred. 
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A65: Bending the coat hanger causes the molecules to heat up. So, some of the Kinetic Energy you have created by bending the wire is being transformed into heat. 
Q66: Can a roller coaster car start on a hill that is 20 meters high and make it up to the top of a second hill that is 40 meters high? Why or why not? 
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A66: Remember that machines are not 100% efficient. The roller coaster car will loose energy through friction and air resistance. It won't even make it up to the top of a second hill exactly the same height as the first. So, NO it won't make it to the top of a 40 meter high hill. 
Q71: What is a perpetual motion machine? 
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A71: A perpetual motion machine is one that keeps on going forever without any additional input of energy. According to what we have learned so far, this is impossible, because machines are not 100% efficient. 
Q72: Define the word “EFFICIENCY.” 
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A72: Efficiency is a quantity, usually expressed as a percentage, that measures the ratio of useful work output to work input. 
Q73: What is the formula for efficiency? 
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A73: Efficiency = Work Output / Work Input 
Q74: Efficiency is measured in what unit? 
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A74: Percent (%) 
Q75: Why is no machine 100% efficient? 
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A75: No machine is 100% efficient because machines loose energy due to friction and heat. 
Q76: Why do all machines need energy input? 
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A76: All machines need energy input because they are not 100% efficient. They loose energy due to heat and friction. 
Q77: You are on a swing. Occasionally you need a push to keep going. Why? 
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A77: You need a push to keep you going on a swing because the swing looses energy due to air resistance, and friction. 
Q78: In an experiment you roll a ball down a ramp and measure Potential and Kinetic Energy. You find that the values for kinetic energy are always just a little less than the values for potential energy. Did you do the experiment wrong? Why or why not? 
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A78: In this experiment although Potential Energy is converted to Kinetic Energy, the ball looses some of its Kinetic Energy due to FRICTION. So, the values will not be exactly the same. 
Q81: What is Work? 
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A81: Work is done when a force causes an object to change its motion or position. 
Q82: What is POWER? 
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A82: Power is the rate at which work is done. 
Q83: What do machines do to forces? 
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A83: Machines change the size and/or direction of forces. 
Q84: List the 6 simple machines. 
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A84: lever, pulley, wheel and axle, inclined plane, wedge, and screw 
Q85: All levers have two things in common. What are they? 
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A85: 
Q86: Inclined planes turn a small input force into a ……… 
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A86: Inclined planes turn a small input force into a large output force. 
Q87: How many simple machines are contained in a compound machine? 
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A87: Compound machines are made of two or more simple machines. 
Q88: What happens to ENERGY when WORK is done? 
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A88: Whenever work is done, energy is transformed or transferred. 
Q89: Potential energy results from what? 
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A89: Potential energy results from the relative positions of objects in a system. 
Q810: Kinetic energy is dependent on two factors. What are they? 
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A810: Kinetic energy depends on both mass and speed. 
Q811: At what level does nonmechanical energy occur? 
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A811: Nonmechanical energy occurs on the level of atoms. 
Q812: Can energy readily change from one form to another? 
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A812: Energy readily changes from one form to another. 
Q813: Can energy be created? Can it be destroyed? 
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A813: Energy can never be created or destroyed. 
Q814: Can a machine do more work than the amount of work required to operate it? 
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A814: A machine can't do more work than the work required to operate it. 