Test #1 -solutions

Test #1 -solutions - Version 043/AACCD – Test#1 –...

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Unformatted text preview: Version 043/AACCD – Test #1 – Antoniewicz – (56445) 1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 2) 5.0 points You’re driving on a straight road (in the + x direction) at a constant speed of 25 m / s. In 11 s, you speed up to 40 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? 1. 35.5 2. 34.0 3. 36.5 4. 35.0 5. 32.5 6. 33.5 7. 34.5 8. 33.0 9. 36.0 10. 37.0 Correct answer: 32 . 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 = 40 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 + 40 m / s 2 = 32 . 5 m / s . 002 (part 2 of 2) 4.0 points How far do you go during this maneuver? 1. 350.0 2. 284.0 3. 357.5 4. 335.0 5. 276.0 6. 438.0 7. 292.0 8. 396.0 9. 288.0 10. 328.5 Correct answer: 357 . 5 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 11 s interval: Δ x = = v avg ,x Δ t = (32 . 5 m / s)(11 s) = 357 . 5 m . 003 9.0 points A rubber ball is dropped from rest onto the floor, and bounces back up to the same height from which it started. Ignore the force of fric- tion due to the air. Which of the following sets of plots most accurately depict this mo- tion? (The force plots depict the force on the ball by the environment.) 1. t y t v y t F y 2. t y t v y t F y correct 3. t y t v y t F y Version 043/AACCD – Test #1 – Antoniewicz – (56445) 2 4. t y t v y t F y 5. t y t v y t F y Explanation: Since there is a constant force, gravity, downward, the plot of the y-position should be parabolic with negative slope whose mag- nitude is increasing over time, until it hits the floor. At this point the slope should switch sign and point upward and decrease in mag- nitude over time. The velocity should be ini- tially 0 m/s since the ball started from rest, and decrease linearly until it hits the floor, at which point it is very quickly given a boost to a positive value, and again continues to de- crease linearly. The force should be always a negative constant value, except for when the ball hits the floor, at which point it should be a narrow positive peak to indicate the brief upward force exerted on the ball by the floor. 004 9.0 points Two students who are late for tests are run- ning to classes in opposite directions as fast as they can. They turn a corner, run into each other head-on, and crumple into a heap on the ground. Using physics principles, es- timate the force that one student exerts on the other during the collision. Assume equal masses of 60 kg for each student, and equal running speeds of 3 m/s. Assume that eachrunning speeds of 3 m/s....
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This note was uploaded on 11/15/2011 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas.

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Test #1 -solutions - Version 043/AACCD – Test#1 –...

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