RCW1 - Recitation ClassWork 1 Physics 203 1. A person sits...

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Unformatted text preview: Recitation ClassWork 1 Physics 203 1. A person sits in the passenger seat of a car that is traveling down a street. Describe the motion of the person as seen by each of the following observers: a. A person sitting in the backseat of the car. b. A pedestrian standing on the sidewalk as the car passes by. c. The driver of a second car moving in the same direction and passing the first car. 2. Review your answers for question 1 and answer the following: a. Do any observers say that the person sitting in the passenger seat of the car was moving? Explain. b. Do any observers say that the person sitting in the passenger seat of the car was not moving? Explain. c. Based on your answers to parts a. and b., explain carefully what it means when an observer says an object is "moving." 3. The idea that different observers see the same object moving differently (called relative motion) needs experimental testing. Consider the following experiment: Marta walks in a westerly direction carrying a ball. Her friends Eric and Joan are watching the ball. a. Use your understanding of relative motion to predict what Eric needs to do to see the ball as not moving. Explain your prediction. b. Use your idea of relative motion to predict what Joan needs to do to see the ball as moving in the easterly direction. Explain your prediction. c. Reproduce this experiment to test your predictions. Use whatever materials you have available to you. d. Make a judgment about whether the idea of relative motion is supported or disproved by your experiments. 4. Ed says "Joan is moving away." a. Explain why this is ambiguous. b. In general, what is needed for an unambiguous description of motion. 5. The illustration below depicts a motion diagram for a given object. Describe in detail a realworld situation that is consistent with this motion diagram. Note that the motion has three distinct parts. The vertical dashed lines separates the parts. v v v v v v v v = 0 6. Imagine performing the following experiments. For each of them, sketch a motion diagram and a force diagram (also known as a freebody diagram) for the cart. a. Steadily push the back of a lowfriction cart along a smooth surface so that it moves faster and faster. b. Stop pushing the cart and let it coast. The cart does not slow down. c. Push gently on the front of the moving cart so that it moves slower and slower and eventually stops. d. Is there a pattern in the directions of the unbalanced force (also called the net force) that other objects exert on v the cart and in the directions of the arrows? Is there a pattern in the directions of the unbalanced force that other objects exert on the cart and the directions of the v arrows on the motion diagrams? e. Use the pattern that you found to formulate a statement relating the force diagram to the motion diagram. v = 0 7. Imagine that you have an air hockey table. It's not working properly though. The air is blowing through the tiny holes in the surface on half of the table only. You place the air hockey puck at rest near the edge of the working end of the table. You hit the puck moderately hard towards the other end of the table. Once it moves onto the broken half of the table is slows down and eventually comes to a stop. Draw a motion diagram and a force diagram for each of the following parts of the puck's motion: a. While the puck is resting on the table, before it was hit. b. While the puck is being hit. c. While the puck is coasting on the working part of the table. d. While the puck is slowing down on the broken part of the table. e. While the puck is resting on the table, after it has stopped. 8. A friend claims that the force diagram at the right describes the forces exerted on a lawn mower during one instant while mowing the lawn, with the mower moving to the right. Is this possible? If so, describe the circumstances under which this is possible and label the force arrows on the diagram. If this isn't possible, explain why not. 9. Imagine that you are holding a tennis ball. You throw it upwards. It slows down, reverses direction, speeds up, then you catch it. Draw a motion diagram and a force diagram for each of the following parts of the ball's motion: a. While you are holding the ball, before you throw it upwards. b. While you are throwing it and it is still touching your hand. c. While the ball is moving upwards, after it has left your hand. d. While the ball is at the highest point in its motion. Hint: Think carefully about this! e. While the ball is moving downwards, before you catch it. f. While you are catching it. y x g. While you are holding the ball, after you have caught it. ...
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This note was uploaded on 06/22/2009 for the course PHYS 1101 taught by Professor Richardson, b during the Fall '08 term at Cornell.

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