# Potential difference question

1. May 25, 2007

### suldaman

Potential difference question....

1. The problem statement, all variables and given/known data

A proton (mass = 1.67 10-27 kg, charge = 1.60 10-19 C) moves from point A to point B under the influence of an electrostatic force only. At point A the proton moves with a speed of 60 km/s. At point B the speed of the proton is 80 km/s. Determine the potential difference Image .

2. Relevant equations
Vb-Va = 0

3. The attempt at a solution
a) +15v
b) -15V
c) -33V
d) +33V
e) -20V

im stumped with this one....any help would be appreciated.

2. May 25, 2007

### Pythagorean

delE = q(delV)

OR

Change in E(energy) = charge*change in V(potential)

for starters

3. May 25, 2007

### Pythagorean

actually, I don't get near any of the answers there. Don't take my word for it, let me look into it more

4. May 25, 2007

### Pythagorean

ok, I did get within .4 of one of the answers there (i wasn't paying attention to units when I calculated last time)

so that way should work, methinx.

5. May 25, 2007

### stunner5000pt

i get within .4 of the answers a well

i guess they want you to round them off

now decide which is right... a or b

6. May 25, 2007

### Pythagorean

if you did it right, you should get either a or b, not both. They are 30 units apart.

7. May 25, 2007

### jackiefrost

I get point b about -14.6 volts relative to point a. Can't tell from the question whether that means answer a or b is correct. Probably b :uhh:

8. May 27, 2007

### cepheid

Staff Emeritus
I didn't bother doing any calculations, but I can tell you the sign of the answer. Think of it this way: the final velocity was greater than the initial velocity, right? So the particle's kinetic energy increased. It moved under the influence of a conservative force solely, so the increase in kinetic energy came at the expense of a(n) ______________(increase/decrease) in potential energy. As a result, considering that the charge is positive, its final electric potential is ______________ (larger/smaller) than its initial electric potential. Therefore, the change in electric potential between the two points (final minus initial) is ______________ (positive/negative).

Fill in the blanks....:tongue2:

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