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# Kinetic Energy

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Joined: Sep 2007
Kinetic Energy

Ok, well, I'm not in AP physics, I'm in honors, but even so I need help.

In our class we are trying to get find the KE and GPE of a rubber ball (those rubber balls that's like 25 cents)

GPE = Mass x Gravity x Height
KE = 1/2 x Mass x Velocity^2

The givens were the Height, the Gravitational Pullt (we're just going to round 9.8 to 10 m/s) and the mass is 0.0235kg.

So the GPE is the one we found out pretty easily, but the KE is the tricky one mainly because of the Velocity. I should probably tell you we are dropping the ball from a free fall so we don't need a timer, however, we need to find the time to get the velocity, so we need to use the Free Fall equation in order to get that.

aaaannnd. that's where i'm stuck at. I can't seem to get the time.

wouldn't the equation be:

Dy = 1/2gt ?

and KE would be
KE = 1/2m(gt)^2?

so to get the time it would be:

(going back to the Dy equation)
t = [(1/2)g]/Dy

Since the Dy is the Height.

right?

capitalization? who the heck came up with this horrible rule?!

[IMG]http://i40.photobucket.com/albums/e201/Ohnn/ID.jpg[/IMG]
[=DarkOrange][=2]my ap equilavent courses:
ib art; ib math sl; ib english

Offline
Joined: Feb 2008

Ok, so let's say A is delta and E is sum
EAMechEnerg=AKE+APotEnerGrav-W+F.L.+APotEnerElastic
so 0=(KEf-KEi)+(PEgf-PEgi) right?
if it's dropped from rest then KEi=0
the PEgf would be 0 as well right?
KEf=1/2*m*V^2
-PEgi=m*g*hi
so KEf=PEgi
1/2mV^2=mghI
what's the displacement? (h)
does that help at all?
I tried :)

I take
AP US 2
Honors Physics
Honors Precalc/Trig
and still can't figure out
how I manage to pass.
???

Offline
Joined: Sep 2007

yea. it did.

thanks!
^^

and a got a 90 on the lab report, so I'm happy. :D
Thanks again.

capitalization? who the heck came up with this horrible rule?!

[IMG]http://i40.photobucket.com/albums/e201/Ohnn/ID.jpg[/IMG]
[=DarkOrange][=2]my ap equilavent courses:
ib art; ib math sl; ib english

Offline
Joined: Feb 2008

oh, great!
no problem:)

I take
AP US 2
Honors Physics
Honors Precalc/Trig
and still can't figure out
how I manage to pass.
???

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