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Conservative/ Non conservative forces problem 
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#1
Mar2712, 01:54 PM

P: 11

Im kind of struggling with some conservative/nonconservative force problems. Someone please help me.
1. The problem statement, all variables and given/known data A 1.8 kg rock is released from rest at the surface of a pond 1.8 m deep. As the rock falls, a constant upward force of 4.3 N is exerted on it by water resistance. Let y=0 be at the bottom of the pond. Calculate the nonconservative work, W nc, done by water resistance on the rock, the gravitational potential energy of the system, U, the kinetic energy of the rock, K , and the total mechanical energy of the system, E , when the depth of the rock below the water's surface is 0 . 2. Relevant equations W=Fd K=0.5(mv)^2 U=mgd E=U+K Wnc=ΔE=EfEi 3. The attempt at a solution I've been going at this one for almost an hour now. I tried finding the final velocity of the rock first since it starts from rest so that I can find its kinetic energy. To find its non conservative work done by water resistance, I used the Work =force *distance formula and multiplied the force of the water resistance by 1.8 m, but that doesn't seem right. To find its gravitational potential energy, I used the U=mgd formula but got the wrong answer for some reason. For the kinetic energy, I used K=0.5(mv)^2 and used the velocity from the first calculation. To find the total mechanical energy, I added up the potential and kinetic energies. Did I do something wrong? Someone please help me. 


#2
Mar2712, 06:27 PM

HW Helper
PF Gold
P: 1,954

I'm not quite sure how to interpret the problem statement on this particular part. Do you know, are you supposed to show the gravitational potential energy when the rock is at the top or bottom? 


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