A 1300 kg. wrecking ball hangs from a 12 m -long cable. The ball is pulled back
ID: 1701284 • Letter: A
Question
A 1300 kg. wrecking ball hangs from a 12 m -long cable. The ball is pulled back until the cable makes an angle of 28.0 with the vertical.
By how much has the gravitational potential energy of the ball changed? U=_________
Express your answer to two significant figures and include the appropriate units.
Can you please help or check the answer...I was marked wrong when I put this answer in 2 sig figs
= 1.5*103 J
RE: change in gravitational potential energy
Answer Details
when the ball is mean position that means horizontal (h = 0) then the intial potential energy,
P.Ei = mgh = 0
if the ball is reaches height 'h' then the final potential energy,
P.Ef = mgh = mgl(1-cas) = 1300*9.8*0.117
= 1491.24 J
therefore P = Pef-Pei =1491.24 J
Explanation / Answer
All that was done by you is correct but you forget to multiply with 'l' in third step from the bottom of answer.
P.Ef = mgl(1 - cos)
= 1300 * 9.8 * 12 * (1 - cos28)
= 1300 * 9.8 * 12 * 0.117
= 17886.96
= 1.8*10^4 J
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