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Unformatted text preview: Bell, Evan – Homework 4 – Due: Feb 13 2005, 11:00 pm – Inst: Furlan 1 This print-out should have 11 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points A car initially travels north and then turns to the left along a circular curve. This causes a package on the seat of the car to slide toward the right side of the car. Which of the following is true of the net force on the package while it is sliding? 1. The force is directed north. 2. The force is directed away from the center of the circle. 3. There is not enough force directed north to keep the package from sliding. 4. There is not enough force tangential to the car’s path to keep the package from sliding. 5. There is not enough force directed toward the center of the circle to keep the package from sliding. correct Explanation: The package is sliding toward the right side of the car, i.e. , it is sliding away from the center of the circle. Thus there is not enough centripetal force to keep the package from sliding. 002 (part 1 of 1) 10 points A ball of mass 20 . 8 g is attached to a cord of length 0 . 559 m and rotates in a vertical circle. The acceleration of gravity is 9 . 8 m / s 2 . What is the minimum speed the ball must have at the top of the circle so the cord does not become slack? Correct answer: 2 . 34056 m / s. Explanation: Basic Concept: Centripetal Acceleration a c = v 2 R Solution: To hold the cord from being slack when the ball is at the top of the circle, the centripetal force must equal the weight of the ball: mg = ma c Since the centripetal acceleration of the ball a c = v 2 R then g = v 2 R and the minimum speed of the ball at this point is v = p g R = q (9 . 8 m / s 2 )(0 . 559 m) = 2 . 34056 m / s 003 (part 1 of 1) 10 points A curve of radius 52 . 9 m is banked so that a car traveling with uniform speed 48 km / hr can round the curve without relying on fric- tion to keep it from slipping to its left or right. The acceleration of gravity is 9 . 8 m / s 2 . 2 . 2 M g μ ≈ θ What is θ ? Correct answer: 18 . 928 ◦ . Explanation: Let : m = 2200 kg , v = 48 km / hr , r = 52 . 9 m , and μ ≈ . Basic Concepts: Consider the free body diagram for the car. The forces acting on Bell, Evan – Homework 4 – Due: Feb 13 2005, 11:00 pm – Inst: Furlan 2 the car are the normal force, the force due to gravity, and possibly friction. μ N N N cos θ mg N sin θ x y To keep an object moving in a circle re- quires a force directed toward the center of the circle; the magnitude of the force is F c = ma c = m v 2 r ....
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This homework help was uploaded on 03/30/2008 for the course PHYS 250 taught by Professor Gallis,michaelro during the Spring '07 term at Pennsylvania State University, University Park.
- Spring '07