
Splung.com Physics Forum Discuss physics or ask questions. Part of the Splung.com physics web site.

View previous topic :: View next topic 
Author 
Message 
keocat
Joined: 13 Mar 2011 Posts: 1 Location: canada

Posted: Sun Mar 13, 2011 11:49 pm Post subject: Electric Potential 


Alright, so I don't really know where to start this problem. I know that there must be some comparison between the two situations, but I don't kno what or where to start to figure it out!
Question:
Long, long ago, on a planet far, far away, a physics experiment was carried out. First, a 0.240 kg ball with zero net charge was dropped from rest at a height of 1.00 m. The ball landed 0.350 s later. Next, the ball was given a net charge of 7.80 \mu C
and dropped in the same way from the same height. This time the ball fell for 0.650 s before landing.
What is the electric potential at a height of 1.00 m above the ground on this planet, given that the electric potential at ground level is zero? (Air resistance can be ignored.)
I believe that V = kq/r or V = qU
Again, I'm not sure how I should be looking at this problem, since I seem to be missing a lot of information. 

Back to top 


hepcj Site Admin
Joined: 23 Jun 2007 Posts: 125

Posted: Tue Mar 22, 2011 11:40 pm Post subject: 


First we need to calculate the force due to gravity when there is no charge on the object. We can use the equations of linear motion.
s = u t + 0.5 g t^2
1 = 0.5 g 0.35^2
which gives g = 16.3265 m/s^2
calculate the acceleration on the object when the charge is added. This will the sum of the force due to gravity and the force in the opposite direction due to the repulsive charge. (it has to act in the opposite direction because the time taken to fall is longer.)
So we have
F = m g h  q E
or
a = m g  q E/m
substitute this expression for acceleration into the equation of motion where the charged object falls:
1 == 0.5 a 0.65^2
and solve for E and it should be 3.57 x 10^5 N/C
from V = E d
3.57 x 10^5 V relative to the zero of potential. 

Back to top 




You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum

© Copyright 2010 Splung.com
