HG_Sol_Practice

HG_Sol_Practice - PHYS 172 — Fall 2010 Exam 2...

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Unformatted text preview: PHYS 172 — Fall 2010 Exam 2 Hand-written Portion (30 points total) Name (Print): Signature: PUID: You will lose points if your explanations are incomplete, if we can't read your handwriting, or if your work is sloppy. Hand-Written Problem: Tossing a Ball You toss a ball (mass = 140 g) straight up into the air. The ball leaves your hand with a speed of 10 m/s, at a height of 1.5 meters above the ground, such that the initial position vector is <O,1.5,0> m. Our unit vectors are defined such that the y—direction points straight up into the air. In this problem you’ll use the energy principle to predict the speed of the ball when it has reached a certain height. You’ll also compute how high the ball will rise before it starts falling back down. Consider two possible choices for "system" and "surroundings". Choice 1: The system includes everything in the universe. Choice 2: The system consists ofjust the ball. All else resides in the surroundings. In parts A—D, assume Choice 2 for the system and surroundings. A. (5 points) The energy principle is AEWem 2 WWW, + Q. Express all of the terms in the energy principle for this selection of system and surroundings. 70 b13673: AK :‘ 6761‘:- w T +WAHL ’l‘ ,4 pl: (132644441 Mlbsuuj her/rm (AK, WEAK-r“) Will/L) AZ A0 15 VVtcLoéaQ‘. B. (5 points) List the external objects that interact significantly with the system. Make a carefully labeled free—body diagram showing the interaction between each object in the surroundings with each object in the system. 1‘ ~ tweet”: Dflfl’C-y E A44 HEAT Puow FEAKTH C. (8 pts) Use the energy principle to find the speed of the ball when it has risen to the position <0, 3, 0> m. Show all steps, clearly identify your initial and final states, indicate any approximations you're making, include units, and circle the final answer. We suggest working with symbols, simplifying the algebra, and then plugging in numbers only at the end. [This will help you in part D]. ___~. *5 _ l 7—— 1 __. h "" I i < o) ~Am310>‘<O) hm»: V Mg LVF "W5 ’1 5 I N b 1—0 00 f /\ <J\ u D. (8 points) Use the energy principle to find the maximum height ofthe ball above the ground. Show all steps, clearly identify your initial and final states, indicate any approximations you‘re making, include units, and circle the final answer. You may quote any results that you derived in part C. Q A x \J AK I WEMJH will“ Mm" ‘92 LSMIO>J (O/'°%fll°> QM 9%: <0) \je) O> [<o/o)o> \ 2, '2. __ Wht , - 3 : \ _ . 79+ : O l E 5" 2+ VL : yr "L ,\_ 103 Z L —l— l g : : (9 (3 {pm 9.9. E. (4 points) If you had taken Choice 1 as system and surroundings, how would your expression for the terms in the energy principle AEWM 2 WWW, + Q have chan ed? N g \UMJC~O / MugT HQCLoDE DOW,I4L_ Wéy [Age/’7 ...
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HG_Sol_Practice - PHYS 172 — Fall 2010 Exam 2...

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