HW #6-2-solutions

# HW #6-2-solutions - pasha(sep635 HW 6-2 Antoniewicz(56445...

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pasha (sep635) – HW 6-2 – Antoniewicz – (56445) 1 This print-out should have 19 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. 001 (part 1 of 4) 2.0 points An object at location h- 20 , 0 , 0 i mmovesto location h- 30 , 0 , 0 i m. While it is moving it is acted on by a constant Force oF h 22 , 0 , 0 i N. How much work is done on the object by this Force? Correct answer: - 220 J. Explanation: W = ~ F · Δ ~ r = F x Δ x + F y Δ y + F z Δ z =(22 N )( - 30 - ( - 20))m = - 220 002 (part 2 of 4) 1.0 points Does the kinetic energy oF the object increase or decrease? 1. Decrease correct 2. Increase 3. There is no change in the kinetic energy oF the ball. Explanation: Consider the update Form oF the Conserva- tion oF Energy: E sys,f = E sys,i + W surr .Th e system is the object, and the surroundings are doing work on the object. The calculated work due to the Force on the object is neg- ative. This means that the initial energy oF the system is greater than the fnal energy oF the system, i.e. the energy oF the system de- creased. The Force acts on the object in a direction that opposes the initial motion oF the object. Thus, the kinetic energy oF the object decreases. 003 (part 3 of 4) 2.0 points Now, consider a di f erent object as it moves From location h- 30 , 0 , 0 i mtolocat ion h- 20 , 0 , 0 i m. While it is moving, it is acted on by a constant Force oF h 22 , 0 , 0 i N. How much work is done on the second object by this Force? Correct answer: 220 J. Explanation: W = ~ F Δ ~ r = F x Δ x + F y Δ y + F z Δ z =(22 N )( - 20 - ( - 30))m =220 004 (part 4 of 4) 1.0 points Does the kinetic energy oF the second object increase or decrease? 1. There is no change in the kinetic energy oF the ball. 2. Increase correct 3. Decrease Explanation: Apply the update Form oF the Conservation oF Energy once again. The work calculated is positive, so the fnal energy state will have a greater value than the initial energy state. 005 (part 1 of 4) 2.0 points AballoFmass0 . 9kgFallsdownward. Initially , you observe it to be 4 . 75 m above the ground. AFter a short time, the ball is just about to hit the ground. During this interval, how much work was done on the ball by the gravitational Force? Use 9 . 8 m s 2 as the acceleration due to gravity. Correct answer: 41 . 895 J. Explanation: W = ~ F · Δ ~ r = F

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pasha (sep635) – HW 6-2 – Antoniewicz – (56445) 2 = - mg ( y f - y i ) = - (0 . 9kg) ± 9 . 8 m s 2 ² (0 - 4 . 75 m) =41 . 895 J 006 (part 2 of 4) 1.0 points Does the kinetic energy of the object increase or decrease? 1.
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## This note was uploaded on 11/17/2011 for the course PHY 303K taught by Professor Turner during the Fall '08 term at University of Texas.

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HW #6-2-solutions - pasha(sep635 HW 6-2 Antoniewicz(56445...

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