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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
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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 value of
v
back into your energy
conservation equation.
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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
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This note was uploaded on 06/12/2011 for the course PHY 131 taught by Professor Rijssenbeek during the Fall '03 term at SUNY Stony Brook.
 Fall '03
 Rijssenbeek
 Circular Motion, Energy, Work

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