quiz4_sp10_sol

quiz4_sp10_sol - Physics 101 Classical Physics Spring 2010...

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Unformatted text preview: Physics 101 Classical Physics Spring 2010 Quiz 4 Instructions : The answer sheets must be handed in as soon as time is called. You have until 9:20am. Answer the following two multiple choice questions. Each question is worth 5 points. 1. A 100 kg man climbs 10 m up a ladder. Which of the following is the minimum number of kilocalories that he could burn off doing this? You should assume that there are 4 J in a calorie. (a) 4000 kCal, (b) 4kCal, (c) 2.5 kCal, (d) 0 kCal, (e) 250 kCal The minimum number of calories will be the amount needed just to increase the man’s gravitational potential energy. So we have U = mg Δ y = (100 kg)(10 m / s)(10 m) = 10000 J. Since the problem says 1 calorie= 4 J, this is 2500 calories or 2.5 kCal. The answer is therefore c . 2. The weight of an object on the moon is 1/6 that of its weight on the Earth. The ratio of the work done on a falling body by gravity on the moon to the same falling body on the Earth is: (a) 6:1, (b) 1:6, (c) 1:1, (d) 1: √ 6 , (e) There is no gravity on the moon, so no work can be done. The weight of an object is mg , where g is the acceleration due to gravity. When an object falls, gravity does work mgd where d is the distance that it travels during the fall. The question says that on the moon, mg is 1/6 of what it is on Earth, so that the work done by gravity must be 1/6 that on the earth. So the answer is b . Please note that as the problem states, an object on the moon has a weight and therefore there MUST BE GRAVITY ON THE MOON. You may also realize this because the astronauts were able to walk on the moon, without floating away. 1 For the following problem, you must show your work to receive full credit. Answer all sections of the problem. 3. A 10 kg block starts out at rest on a frictionless incline whose angle is θ = 30 ◦ with the horizontal. It then travels 1.0 m down the incline (as measured along the incline), then across a 0.5 m-long flat, frictionless surface until in encounters a very large spring whose spring constant is 400 N/m. It compresses the spring from its equilibrium position, at which point the block is temporarily at rest.from its equilibrium position, at which point the block is temporarily at rest....
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quiz4_sp10_sol - Physics 101 Classical Physics Spring 2010...

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