physics 111 hw5

# physics 111 hw5 - sindt(as53996 – HW 5 – opyrchal...

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Unformatted text preview: sindt (as53996) – HW 5 – opyrchal – (11101) 1 This print-out should have 9 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points An 85 N block rests on a table. The sus- pended mass has a weight of 28 N. 85 N 28 N μ s What frictional force is required to keep the blocks from moving? Correct answer: 28 N. Explanation: Given : W 1 = 85 N and W 2 = 28 N . a T N W 1 μ s N a T W 2 Consider the forces then the blocks would first start to move: For block W 2 vertically, F y,net = T-W 2 = 0 For block W 1 horizontally, F x,net = T- μ N = 0 μ N = T = W 1 = 28 N . 002 (part 1 of 2) 10.0 points A car is traveling at 74 . 1 mi / h on a horizontal highway. The acceleration of gravity is 9 . 8 m / s 2 . If the coefficient of friction between road and tires on a rainy day is 0 . 081, what is the minimum distance in which the car will stop? (1 mi = 1 . 609) Correct answer: 690 . 881 m. Explanation: Newton’s second law in the direction of motion gives- f k =- μ k mg = ma Solving for a a =- μ k g (1) The acceleration a may be found from the following kinematics equation with v f = 0: v 2 f = v 2 + 2 ax a =- v 2 2 x (2) Combining equations (1) and (2), we obtain v 2 2 x = μ k g or solving for x , x = v 2 2 μ k g Plugging in the appropriate values, x wet = (33 . 1186 m / s) 2 2(0 . 081) (9 . 8 m / s 2 ) = 690 . 881 m 003 (part 2 of 2) 10.0 points What is the stopping distance when the sur- face is dry and μ dry = 0 . 541?...
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physics 111 hw5 - sindt(as53996 – HW 5 – opyrchal...

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