hour 3-1

# hour 3-1 - University of Minnesota Names: School of Physics...

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Unformatted text preview: University of Minnesota Names: School of Physics and Astronomy Physics 1301, Section 200, Fall 2008 Hour Exam 3: Group Problem (Thursday, October 30, 2008) A movie crew is working in the Badlands of western South Dakota when their car overheats. After they stop to let it cool down, an argument breaks out. They agree they must go easy on the engine, so they can make it back to Rapid City, but they disagree about when the engine works the hardest. As a result, they are unable to agree on a driving strategy. When they see you driving by with a large Minnesota sticker on your car, they flag you down and ask for advice. Caroline says that the work done by engine in accelerating from 0 to 20 km/h is less than the work done by the engine in accelerating from 20 to 30 km/h, so they should drive slowly. Rick says the opposite is true, so they should drive faster. Ted says the work depends on the mass, so they should throw out all the useless stuff. Bloop says the work depends on the acceleration time, so they should just accelerate slowly. [Neglect friction and air resistance.] (a) Assume that the car and contents have a mass of 2,000 kg. How much work is required to accelerate the car from 0 to 20 km/hr in 30 s? How much work is required to accelerate from 20 km/hr to 30 km/hr in 30 s? (4 points) (b) Assume you reduce the total mass of the vehicle by unloading 100 kg. What are the answers to the questions in Part (a)? (4 points) (c) What are the answers to the questions in Part (a), if the acceleration time is increased to 60 s? (4 points) (d) What is the average power required to accelerate from 0 to 20 km/hr in 30 s? What is the average power required to accelerate from 20 km/hr to 30 km/hr in 30 s? (4 points) (e) What is the average force required to accelerate the car from 0 to 20 km/hr in 30 s? What is the average force required to accelerate from 20 km/hr to 30 km/hr in 30 s? (4 points) (f) Assume that the car has a crosssectional area of 2.2 m wide by 1.8 m high. Estimate the force on the car due to drag at a speed of 30 km/h. (5 points) ...
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## This note was uploaded on 10/07/2009 for the course PHYS 1301W taught by Professor Marshak during the Fall '08 term at Minnesota.

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