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Unformatted text preview: johnson (mjj622) HW 3 Coker (56625) 1 This printout should have 24 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. This homework for Chapter 4 covers the last set of material that will be tested on Quiz 1, to be held on September 15 at 7 PM in GAR 0.102. 001 10.0 points The correct, general definitions of velocity and acceleration, in terms of position vector vectorr , are vectorv = dvectorr dt , and vectora = dvectorv dt . During a very short time interval, the velocity of an object changes from vectorv i to vectorv f , as shown. vectorv i vectorv f What is the approximate direction of the acceleration during this time interval? 1. 2. 3. 4. correct Explanation: vectora t = vectorv f vectorv i . vectorv i vectorv f vectora t 002 (part 1 of 2) 10.0 points A particle has vectorr (0) = (4 m) and vectorv (0) = (2 m / s) . If its acceleration is constant and given by vectora = (2 m / s 2 ) ( + ), at what time t does the particle first cross the x axis? Correct answer: 2 s. Explanation: vectorr ( t ) = vectorr (0) + vectorv (0) t + 1 2 vectora t 2 , so vectorr ( t ) = (4 m) + (2 m / s) t +( 1 m / s 2 ) ( + ) t 2 = [(2 m / s) t (1 m / s 2 ) t 2 ] +[4 m (1 m / s 2 ) t 2 ] vectorr ( t ) will not have a y component when 4 m (1 m / s 2 ) t 2 = 0 (1 m / s 2 ) t 2 = 4 m t = 2 s . 003 (part 2 of 2) 10.0 points At what time t is the particle moving parallel to the y axis; that is, in the direction? Correct answer: 1 s. Explanation: vectorr ( t ) = vectorr (0) + vectorv (0) t + 1 2 vectorat 2 vectorv ( t ) = dvectorr d t = vectorv (0) + vectorat , so johnson (mjj622) HW 3 Coker (56625) 2 vectorv ( t ) = (2 m / s)  (2 m / s 2 ) ( + ) t = [(2 m / s) (2 m / s 2 ) t ]  (2 m / s 2 ) t vectorv ( t ) will not have an x component when 2 m / s (2 m / s 2 ) t = 0 t = 1 s . At this time vectorv ( t ) = (2 m / s) parallel to the yaxis. 004 (part 1 of 2) 10.0 points A cannon fires a 0 . 334 kg shell with initial velocity v i = 10 m / s in the direction = 47 above the horizontal. x h 1 m / s 4 7 y y The shells trajectory curves downward be cause of gravity, so at the time t = 0 . 415 s the shell is below the straight line by some verti cal distance h . Your task is to calculate the distance h in the absence of air resistance. On what does h depend (besides g )? 1. It depends only on the initial angle , and does not depend on the flight time t or the initial velocity v i . 2. It is a constant and does not depend on the flight time t or the initial velocity v i or the initial angle ....
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This note was uploaded on 02/10/2011 for the course PHY 303K taught by Professor Turner during the Fall '08 term at University of Texas at Austin.
 Fall '08
 Turner
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