Potential Difference in particle

[kdrobey]

Homework Statement

A particle with a charge of -1.5 µC and a mass of 3.0 x 10-6 kg is released from rest at point A and accelerates toward point B, arriving there with a speed of 50 m/s.

(a) What is the potential difference VB - VA between A and B?

Homework Equations

v=(square root of) -2Qo(Va-Vb)/m

The Attempt at a Solution

everything else is given in the equation, v=50m/s, Q=-1.5 x 10^-6 C, m=3 x 10^-6, but i cannot figure out how to get Va-Vb by itself. I tried squaring both sides which gave me Va2=-4Qo2(Va-Vb)2/m, but from there I'm stuck

 

[kreil]

Isn't it just algebra?

v= \sqrt{ \frac{-2Q_0 (V_a - V_b)}{m}} (square both sides)

v^2 = \frac{-2Q_0 (V_A - V_B)}{m}(multiply/divide to move things around)

-\frac{ v^2 m}{2 Q_0}= V_A-V_B

 

[Redbelly98]

You might try thinking about conservation of energy (that is where the equation you give comes from anyway):

(Change in kinetic energy) = - (Change in electric potential energy)

 

[kdrobey]

oh ok, i'll try that

 

[kdrobey]

i plugged in the numbers and got -3 x 10^-6, but that was not right.

 

[Redbelly98]

I plugged in the numbers (Kreil's last equation in msg #2) and got something else. Try again, be careful about properly entering the numbers into your calculator.

Hint: the answer is a lot larger than 1V.

 

[kdrobey]

ohh, a mental error on my part. got it, thanks!