Q2 Test 1 Study Guide

Work, Kinetic Energy, and Simple Reading: Chapter 10 Quiz on Friday, Nov 2

Work, Energy, and Simple Machines

1. Define work and energy. How are they the same? How are they different? 2. Define the following terms related to simple machines: • Simple • Effort force • Resistance force • Displacement of the effort force • Displacement of the load • Mechanical advantage • Ideal mechanical advantage • Efficiency 3. Clearly explain the difference between the mechanical advantage and the ideal mechanical advantage of a machine. Is it possible for the (actual) mechanical advantage to be larger than the ideal mechanical advantage? 4. Describe how to find the ideal mechanical advantage of a . 5. Describe how to find the (actual) mechanical advantage of a simple machine. 6. Define the work input to a simple machine and the work output from a simple machine. 7. Explain how to determine the work input to and work output from a simple machine. 8. Is it possible for the work output from a simple machine to be greater than the work input? Explain your answer. 9. Define an ideal machine. What is the efficiency of an ideal machine?

Levers

1. Explain why machines are useful even though they cannot create work or energy. There are multiple reasons. 2. On the left, draw a picture of a level for which the effort force is smaller than the resistance force. On the right, draw a picture of a lever for which the effort force is larger than the resistance force. What is different about these two levers (how did you know what to draw)? 3. Define lever arm and torque. 4. Which has a larger mechanical advantage, a short wrench or a long wrench? Why? 5. With which is it easier to apply a specified torque to a bolt, a short wrench or a long wrench? Why? 6. Where should you push to open a heavy door, close to the hinges or close to the swinging edge? Explain. 7. Draw a picture of the easiest way to open a door with a push. Draw a second picture where the force is applied to the same place, but to less effect.

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Q2 Test 1 Study Guide

Types of Simple Machines

For each of the following simple machines

1. Draw a picture of the machine 2. Label the resistance and effort forces 3. Label the displacements of the effort force and of the load 4. Indicate whether and how the machine changes the direction of the effort force 5. Give the relevant equation (or number) for the ideal mechanical advantage of the machine. 6. Give a real-world example of the simple machine in use. • Lever • Fixed pulley • Compound pulley with one fixed pulley and one movable pulley (label the pulleys) • Inclined plane • and Axel

Work Done by a Single Force

1. What is the equation for work done by a constant force along a direction parallel to the force? 2. What is the work done by a constant force when the displacement is perpendicular to the force? 3. Explain what the sign (positive or negative) of the work done by a force means. 4. Determine the sign of the work input to and the work output by a simple machine. 5. For each of the following cases, draw a picture of the situation, include arrows showing the direction of the motion and the direction of the force. Determine whether the force does any work and whether the work done, if any, is positive or negative. Explain your answers. • The force to lift a book • Pushing against a stationary wall • Pushing a box along a rough surface • Pushing a box up a frictionless inclined plane • The force of friction as a drives around a curve at a constant speed

Work Against a Force

1. Explain what it means to say that a force does work against gravity or against friction. 2. Can a force both do work against another force and cause an object to speed up? Give an example and identify the opposing force. 3. Can a force do work against another force while the object slows down? Given an example and identify the opposing force.

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Q2 Test 1 Study Guide

Net Work and Kinetic Energy

1. Define Kinetic Energy 2. Explain what it means to say that a moving object has the ability to do work. Give an example of a moving object exerting a force on a second object and doing work on it. 3. State the work-kinetic energy theorem. 4. Explain the difference between the work done on an object by a single force and the net work done on an object. 5. Explain how to find the net work done on an object. There are two ways, explain both. 6. Give two examples where the net work done on an object is negative. 7. Give two examples where the net work done on an object is positive. 8. Give two examples where the net work done on an object is zero.

Application Questions

1. Imagine that you are pushing a box across a rough surface. Compare the forces of your push to the force of friction (1) when the box is speeding up, (2) when the box is traveling at a constant velocity, (3) when the box is slowing down. In each case, is the net work positive, negative, or zero? Does the kinetic energy of the box increase, decrease, or stay the same? 2. Using the concepts of work and kinetic energy, explain why a fast-moving car takes a longer distance to break to a stop than a slower car does. 3. Imagine that you are using a lever to lift a load. If the effort force matches the weight of the load, then what is the total work done on the load? What forces act on the load and what is the sign (+, -, 0) of the work done by each. 4. Now you want to use the lever to catapult the load. What should you do? Use Newton’s second law to explain why this works.

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