Circular Motion and Gravity (exam 2)

# Circular Motion and Gravity (exam 2) - Circular...

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Circular Motion/Gravity Concept Questions CTCirc-1. A particle is moving along the path shown, with constant speed. Its velocity vector at two different times is shown. What is the direction of the acceleration when the particle is at point X? Answer: to the left (A)

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CTCirc-2. A rider in a "barrel of fun" finds herself stuck with her back to the wall. Which diagram correctly shows the forces acting on her? A B C D E Answer: A The person is moving in a circle, therefore she is accelerating toward the center of the circle. Therefore, there must be a net force acting on her toward the center of the circle. That force is the normal force of the wall pressing against her back. There is no outward "centrifugal force". Centrifugal forces are examples of "fictitious forces" or pseudo-forces. Such forces do not exist. (Sometimes pretending such forces exist makes problem-solving mathematically easier. But in my opinion, they also cause terrible confusion.)

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CTCirc-3. A race car travels around the track shown at constant speed. Over which portion of the track is the magnitude of the acceleration the smallest? A) From 1 to 2 B) From 3 to 4 C) Neither of these D) Both of these Answer: Neither of these. The acceleration is zero along the straight line portions of the track.
CTCirc-4. A bucket containing a brick is swung in a circle at constant speed in a vertical plane as shown. The bucket is swung fast enough that the brick does not fall out. The net force on the brick as it is swung has maximum magnitude at position. A) T op. B) B ottom. C) R ight D) The net force has the same magnitude at all positions Answer: The net force must have the same magnitude since F net = m a = m v 2 /R. Since the acceleration is constant in magnitude, the net force must also be constant in magnitude (and always pointed toward the center). Consider the normal force exerted on the brick by the bucket when the bucket is at the three positions shown: R, T, B. The magnitude of the normal force is a minimum at position. .. A) T op. B) B ottom. C) R ight D) The normal force has the same magnitude at all positions. Answer: Normal force has minimum magnitude at the top. See the free-body diagrams. F net always has the same magnitude and points toward the center. The weight always has the same magnitude (mg) and always points down. The net force is the vector sum of the normal force and the weight.

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CTCirc-5. A car of mass m, traveling at constant speed, rides over the top of a hill. The magnitude of the normal force N of the road on the car is. . A) greater than the weight of the car, N > mg.

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## This note was uploaded on 05/25/2008 for the course PHYS 2010 taught by Professor Dubson during the Fall '06 term at Colorado.

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Circular Motion and Gravity (exam 2) - Circular...

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