# Mechanics: Potential energy

• Mar 7th 2009, 07:24 AM
AshleyT
Mechanics: Potential energy
Very basic but i don't understand it... :(
Quote:

A particle of mass 2kg falls freely from rest. Calculate kinetic energy when it has descended 20 meters.
Answer is 392J and i get 392000J.

But i just did 2000(weight) x 9.8(gravity) x 20(distance)
And i think thats wrong...well it must be because the answer i have is wrong lol.

• Mar 7th 2009, 07:45 AM
running-gag
Hi

The weight must be expressed in kg and not in g
BTW gravity is 9.8 N/kg ... (Wink)
• Mar 7th 2009, 10:02 PM
AshleyT
Quote:

Originally Posted by running-gag
Hi

The weight must be expressed in kg and not in g
BTW gravity is 9.8 N/kg ... (Wink)

tyvm:)
• Mar 7th 2009, 11:37 PM
CaptainBlack
Quote:

Originally Posted by AshleyT
Very basic but i don't understand it... :(

Answer is 392J and i get 392000J.

But i just did 2000(weight) x 9.8(gravity) x 20(distance)
And i think thats wrong...well it must be because the answer i have is wrong lol.