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Unformatted text preview: Niu (qn269) – HW05 – Tsoi – (58020) 1 This print-out should have 23 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 2) 10.0 points Consider a bungee cord of unstretched length L = 27 m. When the cord is stretched to L > L it behaves like a spring and obeys Hooke’s law with the spring constant k = 26 N / m. However, unlike a spring, the cord folds instead of becoming compressed when the distance between its ends is less than the unstretched length: For L < L the cord has zero tension and zero elastic energy. To test the cord’s reliability, one end is tied to a high bridge (height H = 162 m above the surface of a river) and the other end is tied to a steel ball of weight mg = 100 kg × 9 . 8 m / s 2 . The ball is dropped off the bridge with zero initial speed. Fortunately, the cord works and the ball stops in the air before it hits the water — and then the cord pulls it back up. Calculate the ball’s height h bot at the lowest point of its trajectory. For simplicity, neglects the cord’s own weight and inertia as well as the air drag on the ball and the cord. Answer in units of m. 002 (part 2 of 2) 10.0 points What is the upward acceleration of the ball at the lowest point? Answer in units of m / s 2 . 003 10.0 points When an automobile moves with constant ve- locity, the power developed is used to over- come the frictional forces exerted by the air and the road. If the engine develops 40 hp, what total frictional force acts on the car at 24 mph?...
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This note was uploaded on 09/01/2009 for the course PHY M taught by Professor Staff during the Spring '09 term at University of Texas.
- Spring '09