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How many joules of PE does a 12 kg rock have after falling from a 76 m cliff and reaches 7 m/s?

Guest May 4, 2017
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"How many joules of PE does a 12 kg rock have after falling from a 76 m cliff and reaches 7 m/s?"

 

E = PE + KE    E is total energy, PE is potential energy, KE is kinetic energy.

 

Top of cliff:  E = 12*9.8*76 + 0 joules

 

E stays constant so when velocity is 7 m/s

 

12*9.8*76 = PE + (1/2)*12*7^2

 

PE = 12*9.8*76 - (1/2)*12*7^2 or PE ≈ 9314 joules

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Alan  May 5, 2017

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