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HW 6 Tips FINAL - HW 6 Tips PHY 131 Sect 10 11 15 Fall 2010...

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1 HW 6 Tips; PHY 131 Sect. 10, 11, 15; Fall 2010 Prof. Pascuzzi HW 6 covers Chapters 7 and 8; Work, Energy, Energy Conservation (plus a little Circular Motion) Information you may need; m/s 2 Important steps in solving Energy Conservation problems; 1) Energy conservation means that the total energy of the closed system remains unchanged, and is the same numerical value at all points in the problem. Therefore, get into the habit of labeling different locations in the problem with different letters (like A, B, C …etc.). 2) Get into the habit of immediately writing down the law of energy conservation at each point, which will even tually look like this; etc…. 3) Next, decide which, if any, variable (such as v or h ) might be zero, then cancel out the corresponding terms (such as KE or GPE ). Sometimes, note that the mass m can cancel, which is often why it is not given! 4) Solve the equation for the variable you want, then substitute the numbers at the end to get your desired quantity. 5) HINT: There may be many occasions when you’ll have to first apply the rules of circular motion first to obtain a velocity (such as a roller coaster with vertical circle, or other unusual circular problem), which means this must be done as well; . Then, you’ll most likely be required to substitute the v alue of v back into your energy conservation equation.
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2 Problem 7.5 “Work done Mowing the Lawn” a) This is a straightforward application of the definition of work; . Think about the calculation of the work done when just moving along one path down the entire yard, and then think about how you will calculate the total number of paths you travel. Then, once you have the work done for one path, just multiply by the number of paths to get the total work. This is problem #5 in Ch. 7, pg. 177. Problem 7. 11 “Man Pushing the Piano” The wording of this problem is a bit unclear. The piano is actually moving downhill, however it is not accelerating and the person is just allowing it to move down the incline at CV. The impression given is that the man is either just holding the piano, or is attempting to push it uphill, neither of which is correct.
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