Posted by Anonymous on Tuesday, September 27, 2011 at 7:09pm.
A 0.28kg stone is held 1.5 m above the top edge of a water well and then dropped into it. The well has a depth of 4.8 m.
(a) Taking y = 0 at the top edge of the well, what is the gravitational potential energy of the stone–Earth system before the stone is released?
J
(b) Taking y = 0 at the top edge of the well, what is the gravitational potential energy of the stone–Earth system when it reaches the bottom of the well?
J
(c) What is the change in gravitational potential energy of the system from release to reaching the bottom of the well?
J

Physics  Henry, Thursday, September 29, 2011 at 3:25pm
a. PE = mgh = 0.28 * 9.8 *1.5 = 4.1J.
b. PE = 0.28 * 9.8 * 4.8 = 13.2 Joules.
c. Change = mg(h1+h2)  0 =
0.28 * 9.8 * (1.5+4.8)  0 = 17.3J.

Physics  Angat Vora, Wednesday, March 28, 2012 at 7:50pm
Actually,
** GPE = mgh
a) GPE = mgh
as height of well is taken to be area of 0 GPE.
sign is positive.
GPE = mgh = 0.28*9.8*1.5
b) GPE = mgh
as height is now below area of 0 GPE, h changes to h.
therefore sign is negative
GPE = 0.28*9.8*(4.8)
c) GPE = mgh
here, mg(h1h2)
therefore,
GPE = 0.28*9.8*(1.54.8)
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