Electric Potential related question

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Homework Help Overview

The discussion revolves around a physics problem involving electric potential and motion under the influence of gravity and an electric field on planet Tehar. The original poster describes a scenario where a charged ball is thrown upward and seeks to determine the potential difference related to its trajectory.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to use kinematic equations to find the distance and acceleration but expresses uncertainty about how to incorporate the electric field's effect. Some participants suggest considering the forces acting on the ball and using Newton's second law to find the effective acceleration.

Discussion Status

Participants are exploring various kinematic equations and questioning the assumptions made about the forces involved. There is a recognition that the time of flight and the effects of the electric field need to be integrated into the calculations. Some guidance has been offered regarding the use of free-body diagrams and the need for a clearer approach to the problem.

Contextual Notes

There is a mention of imposed homework rules that encourage showing work without providing direct answers. Participants express frustration over perceived lack of information and clarity in the discussion.

kfan321
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On planet Tehar, the free-fall acceleration is same as that on Earth, but there is also a strong downward electric field that is uniform close to the planet's surface. A 2 kg ball having a charge of 5 uC is thrown upward at a speed of 20.1 m/s. It hits the ground after an interval of 4.1 sec. What is the potential difference between the starting point and the top of the trajectory?
Well my plan was to use V = E d
So I need to find E and d and I'll have the problem solved.
I used V2^2 = V1^2 + 2ad
v2 is 0, v1 is 20.1, and i used 9.8 for a.
So d came out to 20.6. But I don't think that's correct because I didnt account for the acceleration due to the electric field? So how do I do that?
To solve for E, I wanted to use F/q but not enough info given. Thought about (KQ)/r^2 but not sure if this scenario can be considered point charges...
 
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Due to the electric field, now effective accelaration is changed. Use Newton's second low to find a. (Hint: What are the two forces now acting on the object?)
 
Well you really haven't said anything I don't already know. I've said force gravity and electric field will deccelerate the ball... and that's where I am stuck
 
kfan321 said:
Well you really haven't said anything I don't already know. I've said force gravity and electric field will deccelerate the ball... and that's where I am stuck

Did you draw a free-body diagram?
As you have determined, a is an unknown. d is also unknown. So, your single kinematic equation is not sufficient to find d. Note that you have not used the information about the time of flight. Is there another applicable kinematic equation that can be used here?
 
i've tried d = v1t + .5 at^2
still have 2 variables. So I did a system of equations with the first kinematic equation. Subbing d into a, hoping to find the new a and it came out to -9.8. lol...

...I'm all for not doing other peoples homework for them, but you guys are hiding the info like it's some top FBI confidential document.
 
kfan321 said:
i've tried d = v1t + .5 at^2
still have 2 variables. So I did a system of equations with the first kinematic equation. Subbing d into a, hoping to find the new a and it came out to -9.8. lol...
If you do things algebraically, you might find a single equation with one unknown. (That is, there may be a simpler starting point.)

kfan321 said:
...I'm all for not doing other peoples homework for them, but you guys are hiding the info like it's some top FBI confidential document.

In "Homework, Coursework, & Textbook Questions", you are nudged toward (but not given) the answer... but you have to show your work.
 
using the 2 kinematic equations previously

0 = v1^2 + 2*a*v1*t + a^2 * t^2

this is what I've done on post #5, i knew everything except a in that equation, so I solved for it and it came out to -9.8. Which can't be right b/c of the field, so where did I go wrong?
 
kfan321 said:
v2 is 0

Why is this true?
 
b/c at the top of the trajectory, it's 0 m/s, and I use time as 2.05 instead of 4.1...
But now I think about it, time shouldn't be half... Great, back to square one.

You know what, nvm the thread. I think I am better off figuring it out myself.
 

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