conservation of energy

Physics
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a rock falls 30 m. its KE before it strikes the ground is 4,392 J. what is the mass of the rock? 

Sep 10th, 2015

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rock falls from 30 m

at height of 30 m  it potential energy =mgh=m*10*30            ( i have taken g=10m/s^2 you can use 9.8)

                                                          =300m J

at ground kinetic energy =4392


Potential energy of rock is totally converted kinetic energy

4392=300m

m=14.64 kg


if answer is wrong discusss.

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Sep 10th, 2015

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