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Unformatted text preview: chauhan (mmc2762) – Ch2H2 – turner – (56910) 1 This printout should have 18 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 2) 10.0 points You’re driving on a straight road (in the + x direction) at a constant speed of 25 m / s. In 8 s, you speed up to 42 m / s to pass a truck. Assuming that your car speeds up at a con stant rate (constant force by the road on the tires), what is your average x component of velocity v avg ,x during this maneuver? Correct answer: 33 . 5 m / s. Explanation: Since the car speeds up at a constant rate, we just need to consider the endpoints, when the car was traveling v i,x = 25 m / s and v f,x = 42 m / s . We calculate the average x component of ve locity as follows: v avg ,x = v i,x + v f,x 2 = 25 m / s + 42 m / s 2 = 33 . 5 m / s . 002 (part 2 of 2) 10.0 points How far do you go during this maneuver? Correct answer: 268 m. Explanation: Again, the fact that the acceleration is con stant simplifies things. We can just treat this situation as though we were actually moving at the average speed for the 8 s interval: Δ x = = v avg ,x Δ t = (33 . 5 m / s)(8 s) = 268 m . 003 (part 1 of 3) 0.0 points On a straight road (taken to be in the + x direction) you drive for an hour at v 1 ,x = 40 km / h , then quickly speed up to v 2 ,x = 120 km / h and drive for an additional two hours. How far do you go (Δ x )? Correct answer: 280 km. Explanation: To find the total distance traveled, we have to consider the two speeds separately: Δ x = v 1 ,x Δ t 1 + v 2 ,x Δ t 2 = (40 km / h)(1 h) + (120 km / h)(2 h) = 280 km . 004 (part 2 of 3) 0.0 points What is your average x component of velocity ( v avg ,x )? Correct answer: 93 . 3333 km / h. Explanation: We can’t simply take the arithmetic mean in this case, because the car did not accelerate at a constant rate between the initial and final speeds. Instead, we have to take a weighted average, considering the two speeds and how long the car spent at each speed: v avg ,x = v 1 ,x t 1 + v 2 ,x t 2 t 1 + t 2 = (40 km / h)(1 h) + (120 km / h)(2 h) 2 h + 1 h = 93 . 3333 km / h . 005 (part 3 of 3) 0.0 points chauhan (mmc2762) – Ch2H2 – turner – (56910) 2 Is v avg ,x equal to the arithmetic average of your initial and final values of v x ?...
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This note was uploaded on 04/03/2012 for the course PHYSICS 303K taught by Professor Antoniewicz during the Spring '11 term at University of Texas.
 Spring '11
 Antoniewicz
 Physics

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