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HW2Solutions

# HW2Solutions - Hopkins Timothy Homework 2 Due 8:00 am Inst...

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Hopkins, Timothy – Homework 2 – Due: Feb 19 2008, 8:00 am – Inst: Robert Criss 1 This print-out should have 20 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 4) 10 points A sled is pulled up to the top of a hill. The sketch below indicates the shape of the hill. At the bottom of the hill the sled has a speed | v | and a kinetic energy K (the energy due to the sled’s motion). In every case fric- tion and air resistance are so small they can be ignored. The sled is pulled up a steeper hill of the same height as the hill described above, and allowed to slide down the hill. How will the velocity of the sled at the bottom of the hill compare to that of the sled at the bottom of the original hill? 1. None of these descriptions is correct. 2. The speed at the bottom is greater for the original hill because the sled travels fur- ther. 3. The speed at the bottom is the same for both hills. correct 4. The speed at the bottom is greater for the steeper hill. 5. There is not enough information given to say which speed at the bottom is faster. Explanation: By energy conservation, the speed is pro- portional to the square root of the height of the hill. 002 (part 2 of 4) 10 points Compare the kinetic energy (energy of mo- tion) of the sled at the bottom of the original hill and of the steeper hill in part 1. 1. The kinetic energy of the sled at the bottom is greater for the steeper hill. 2. There is not enough information given to say which kinetic energy of the sled at the bottom is greater. 3. None of these descriptions is correct. 4. The kinetic energy of the sled at the bottom is the same for both hills. correct 5. The kinetic energy of the sled at the bottom is greater for the original hill. Explanation: The same reason as Part 1. 003 (part 3 of 4) 10 points The sled is pulled up a higher hill that is less steep than the original hill described in part 1. How does the speed of the sled at the bot- tom of the hill (after sliding down) compare to that of the sled at the bottom of the original hill? 1. The speed at the bottom is greater for the higher hill. correct 2. There is not enough information given to say which speed at the bottom is faster. 3. The speed at the bottom is greater for the original hill because the sled travels fur- ther. 4. None of these descriptions is correct. 5. The speed at the bottom is the same for both hills. Explanation: The same reason as Part 1. 004 (part 4 of 4) 10 points For the higher hill that is less steep, how does the kinetic energy of the sled at the bottom of the hill after slid downing compare to that of the original hill?

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Hopkins, Timothy – Homework 2 – Due: Feb 19 2008, 8:00 am – Inst: Robert Criss 2 1. The kinetic energy of the sled at the bot- tom is greater for the higher hill. correct 2. None of these descriptions is correct.
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