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UNCG / Physics / PHY 101 / concept development practice page 9-2

concept development practice page 9-2

concept development practice page 9-2

Description

School: University of North Carolina - Greensboro
Department: Physics
Course: Physics 101
Term: Fall 2016
Tags: Force, hewitt, Physics, paul, conceptual, practice, development, page, Concept, and Car
Cost: 10
Uploaded: 05/09/2017
16 Pages 1949 Views 0 Unlocks
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How is the size of the round platform and train speed related to the amount of time that passengers have for boarding?




Why is the stairway located at the center of the platform?




If there is to be no relative motion between the train and the edge of the platform, how fast must the train move compared to the rim speed of the rotating platform?



Uniform Circular  Motion Some Conceptual Activities from Conceptual Physics by Paul Hewitt Monday, January 10, 20111If you want to learn more check out math tutor dvd torrent
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. Most energy of train systems is used in starting and stopping. The  rotating train platform design saves energy, for people can board or  leave a train while the train is still moving. Study the sketch and  convince yourself that this is true. The small circular platform in the  middle is stationary, and is connected to a stationary stairway. a. If there is to be no relative motion between the train and the edge of  the platform, how fast must the train move compared to the rim  speed of the rotating platform? b. Why is the stairway located at the center of the platform? From Paul Hewitt’s Conceptual Physics. Concept-Development Practice Page 9-1. Monday, January 10, 20112. The design below shows a train that makes round trips from Station  A to Station B in a continuous loop. a. How is the size of the round platform and train speed related to the  amount of time that passengers have for boarding? b. Why would this rotating platform be impractical for high-speed  trains? From Paul Hewitt’s Conceptual Physics. Concept-Development Practice Page 9-1. Monday, January 10, 20113. Here are some people standing on a giant rotating platform in a fun  house. In the view shown, the platform is not rotating and the people  stand at rest. When the platform rotates, the person in the middle stands as before.  The person at the edge must lean inward as shown. Make a sketch of the  missing people to show how they must lean in comparison. From Paul Hewitt’s Conceptual Physics. Concept-Development Practice Page 9-1. Monday, January 10, 20114. The sketch at the left shows a stationary container of water and some  floating toy ducks. The sketch at the right shows the same container  rotating about a central axis ay constant speed. Note the curved  space of the water. The duck in the center floats as before. Make a  sketch to show the orientation of the other two ducks with respect to  water surface. From Paul Hewitt’s Conceptual Physics. Concept-Development Practice Page 9-1. Monday, January 10, 20115. Consider an automobile tire half-filled with water. In the cross-sectional  views below the left-hand sketch shows the water surface when the tire is  not rotating. The right hand sketch shows the water surface when the tire  and water rotate about its central axis. Now suppose the tire is rotating about the same axis while orbiting in outer  space. Draw the shape of the water surface in the cross-sectional view below. In your mind, scale up the rotating tire model to a rotating space habitat  orbiting in space. If teh space habitat were half filled with water, could  inhabitants float on the surface as they do here on earth? Discuss. From Paul Hewitt’s Conceptual Physics. Concept-Development Practice Page 9-1. Monday, January 10, 2011Newton’s 2nd law, a = F/m, tells us that net force and its corresponding  acceleration are always in the same direction. (Both force and acceleration  are vector quantities). But force and acceleration are not always in the  direction of velocity (another vector). 6. You’re in a car at a traffic light. The car turns green and the driver  steps on the gas. a. Your body lurches [ forward , not at all , backward ] b. The car accelerates [ forward , not at all, backward ] c. The force on the car acts [ forward , not at all, backward ] The sketch shows  the top view of the  car. Note the  directions of the  velocity and  acceleration vectors. From Paul Hewitt’s Conceptual Physics. Concept-Development Practice Page 9-2. Monday, January 10, 20117. You’re driving along and approach a stop sign. The driver steps on  the brakes. a. Your body lurches [ forward , not at all , backward ] b. The car accelerates [ forward , not at all, backward ] c. The force on the car acts [ forward , not at all, backward ] The sketch shows  the top view of the  car. Note the  directions of the  velocity and  acceleration vectors. From Paul Hewitt’s Conceptual Physics. Concept-Development Practice Page 9-2. Monday, January 10, 20118. You continue driving, and round a sharp curve to the left at constant  speed. a. Your body leans [ inward , not at all , outward ] b. The direction of the car’s acceleration is  [ inward , not at all, outward ] c. The force on the car acts [ inward , not at all, outward ] Draw vectors for the  velocity and  acceleration of the  car. 9. In general, the directions of lurch and acceleration, and therefore the  directions of lurch and force are [ the same , not related ,  opposite ] From Paul Hewitt’s Conceptual Physics. Concept-Development Practice Page 9-2. Monday, January 10, 201110.The whirling stone’s direction of motion keeps changing. a. If it moves faster, its direction changes [ faster , slower ] b. This indicates that as speed increases, acceleration  [ increases , decreases , stays the same ] From Paul Hewitt’s Conceptual Physics. Concept-Development Practice Page 9-2. Monday, January 10, 201111.Consider whirling the stone on a shorter string -- that is, of smaller  radius. a. For a given speed, the rate that the stone changes direction is  [ less , more , the same ] b. This indicates that as the radius decreases, acceleration  [ increases , decreases , stays the same ] From Paul Hewitt’s Conceptual Physics. Concept-Development Practice Page 9-2. Monday, January 10, 201112.A rock tied to a post moves in a circle at constant speed on a  frictionless horizontal surface. All the forces acting on the rock are  shown: Tension T, support force n by the table, and the force due to  gravity W. a. The vector responsible for the circular motion is ________________. b. The net force on the rock is ________________. From Paul Hewitt’s Conceptual Physics. Concept-Development Practice Page 9-2. Monday, January 10, 201113.In this case, the rock is tied to a string and swings in a circular path  as shown. It is not resting on a surface. No friction. Use the  parallelogram rule and find the resultant vectors T and W. a. What is the direction of the resultant of T and W?  _________________________________________________________ b. Does this resultant lie in the plane of the circular path? _________ c. Is this resultant also the horizontal component of T? __________ d. Is the resultant T + W (or the horizontal component of T) a  centripetal force? ___________ From Paul Hewitt’s Conceptual Physics. Concept-Development Practice Page 9-2. Monday, January 10, 201114.In the case shown below, the rock rides on a horizontal disk that  rotates at constant speed about its vertical axis (dotted line). Friction  prevents the rock from sliding. a. Draw and label vectors for all forces that act on the rock. b. Which force is centripetal? __________ c. Which force provides the net force? __________ d. Why do we not say the net force is zero?  ____________________________________________________________ From Paul Hewitt’s Conceptual Physics. Concept-Development Practice Page 9-2. Monday, January 10, 201115.Now the rock is held in place by friction against the inside wall of the  rotating drum. Draw and label vectors for all forces that act on the  rock. a. Which force is centripetal? __________________ b. Which force provides the net force? _____________________ From Paul Hewitt’s Conceptual Physics. Concept-Development Practice Page 9-2. Monday, January 10, 201116.More challenging: This time the rock rests against the frictionless  inside wall of a cone. It moves with the cone, which rotates about its  vertical axis (dotted line). The rock does not slide up or down in the  cone as it rotates. Draw and label vectors for all forces that act on the  rock. a. Should the resultant force lie in the  plane of the circular path? ________ b. Why?  ________________________________ ________________________________ ________________________________ From Paul Hewitt’s Conceptual Physics. Concept-Development Practice Page 9-2. Monday, January 10, 2011

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