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About energy

  • Thread starter lingling
  • Start date
22
0
1. Homework Statement

A stone of mass 2 kg is projected horizontally with a speed of 20 m/s from a cliff which is 15 m above the ground. Find the energy possessed by the stone just before touching the ground.

A. 400J
B. 500J
C. 600J
D. 700J

2. Homework Equations



3. The Attempt at a Solution
I can't get the answer. How can I achieve it?
I think 'just before touching the ground' means when the stone is still moving, but I don't know the velocity at this instant. And at the same time, the stone is losing potential energy, how can I manage this?
 

Hootenanny

Staff Emeritus
Science Advisor
Gold Member
9,598
6
HINT: Inital Energy = Final Energy

Consider 'just before the stone touches the ground' to be the stone has actually hit the ground but not lost any kinetic energy, the instant the stone touches the ground.
 
22
0
Ah..... I've got it!
Thanks a lot!
 

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