35_new - Ch2-HW2 florin (56950) This print-out should have...

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1 This print-out should have 18 questions. Multiple-choice 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 30 m / s. In 8 s, you speed up to 44 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: 37 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 = 30 m / s and v F ,X = 44 m / s . We calculate the average x component of ve-locity as follows: v avg ,X = v I ,X + v F ,X 2 = 30 m / s + 44 m / s 2 = 37 m / s . 3 (part 2 of 2) 10.0 points How far do you go during this maneuver? Correct answer: 296 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: x = = v avg ,X t = (37 m / s)(8 s) = 296 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 = 55 km / h , then quickly speed up to v 2 ,X = 115 km / h and drive for an additional two hours. How far do you go (Δ x )? Correct answer: 285 km. Explanation: To find the total distance traveled, we have to consider the two speeds separately: x = v 1 ,X t 1 + v 2 ,X t 2 = (55 km / h)(1 h) + (115 km / h)(2 h) = 285 km . 4 (part 2 of 3) 0.0 points What is your average x component of velocity ( v avg ,X )? Correct answer: 95 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 = (55 km / h)(1 h) + (115 km / h)(2 h) 2 h + 1 h = 95 km / h . 5
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35_new - Ch2-HW2 florin (56950) This print-out should have...

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