Find Energy of 2kg Stone After Projection from 15m Cliff

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Homework Help Overview

The problem involves a stone of mass 2 kg projected horizontally from a height of 15 m. Participants are tasked with determining the energy of the stone just before it touches the ground, considering both its kinetic and potential energy at that moment.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to understand the relationship between potential and kinetic energy as the stone falls. They express uncertainty about the velocity of the stone just before impact and how to account for the loss of potential energy.

Discussion Status

Some participants have offered hints regarding the conservation of energy principle, suggesting that the total initial energy equals the total final energy. However, the discussion does not reach a consensus, as the original poster continues to seek clarity on the problem setup.

Contextual Notes

The original poster's confusion stems from interpreting the phrase "just before touching the ground" and how it relates to the stone's kinetic energy at that instant. There is also an implied need to consider the transition from potential to kinetic energy during the fall.

lingling
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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

Homework Equations





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?
 
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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.
 
Ah... I've got it!
Thanks a lot!
 
lingling said:
Ah... I've got it!
Thanks a lot!
My pleasure :smile:
 

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