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 Energy and Work Energy and Work Physics Help Forum Oct 29th 2008, 09:11 PM #1 Junior Member   Join Date: Oct 2008 Posts: 8 Work and Energy Question Rene, whose mass is 85 kg, skis down a hill, passing a point Z with a kinetic energy of 9700J. If friction is ignored, to what maximum height, h, can Rene ski? Relevant Equations ΔEp = -ΔEk -ΔEp = ΔEk for relevant equations I am not quite sure because one teacher showed us to use the one above while another teacher showed us the one below. Attempt For this question I am assuming that you use the above one because you are trying to find the final height "hf" for this question. So what I did was: -ΔEp = ΔEk -(mghf - mghi) = (1/2)mvf(squared) - (1/2)mvi(squared) I continued to plug in the numbers and isolate the final height "hf", but then I encountered a problem because I don't know what the final velocity is "vf" so I don't know how to proceed.   Oct 31st 2008, 07:51 PM   #2
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 Originally Posted by Inertialforce Question Rene, whose mass is 85 kg, skis down a hill, passing a point Z with a kinetic energy of 9700J. If friction is ignored, to what maximum height, h, can Rene ski? Relevant Equations ΔEp = -ΔEk -ΔEp = ΔEk for relevant equations I am not quite sure because one teacher showed us to use the one above while another teacher showed us the one below. Attempt For this question I am assuming that you use the above one because you are trying to find the final height "hf" for this question. So what I did was: -ΔEp = ΔEk -(mghf - mghi) = (1/2)mvf(squared) - (1/2)mvi(squared) I continued to plug in the numbers and isolate the final height "hf", but then I encountered a problem because I don't know what the final velocity is "vf" so I don't know how to proceed.
Using
$\displaystyle 9700= mv^2/2$
then you can get the velocity at that time

-ΔEp = ΔEk
$\displaystyle -mgh=mv^2/2$
$\displaystyle h=-v^2/2g$  Tags energy, work Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Physics Forum Discussions Thread Thread Starter Forum Replies Last Post NSB3 Advanced Mechanics 1 Nov 12th 2014 12:03 PM FlexedCookie Kinematics and Dynamics 4 Mar 15th 2011 02:42 AM sake Kinematics and Dynamics 14 May 14th 2009 09:47 PM hriday Advanced Mechanics 3 May 1st 2009 10:10 AM Morgan82 Advanced Mechanics 1 Nov 10th 2008 02:52 AM