How Is the Magnitude of an Electric Field Calculated from Electron Displacement?

[stylez03]

Homework Statement

An electron is released from rest in a uniform electric field. The electron accelerates vertically upward, traveling 4.50 m in the first 3.00\;\mu{\rm s} after it is released.

What is the magnitude of the electric field?

Homework Equations

F = 1/4*pi*e_o * |q| / r^2 for single point charge

e_o = 8.85 * 10^-12

Mass of electron = 9.109 * 10 ^-31

The Attempt at a Solution

1/(4*pi*8.85 * 10^-12) * ( |9.109 * 10 ^-31| / (4.50)^2 )

The online system said the solution was incorrect.

 

[marcusl]

Note the problem hints at an acceleration; you'll need to calculate the aveage acceleration of the particle, and then use Newton's second law to relate it to the force applied by the field. You need to account for another force here too; do you know what it is? Then you need an equation that relates the net force to both charge and electric field. As an aside, your first equation gives the force between two point charges, which is not the situation here, and in any case it is incorrect as written.

 

[cclawfjj]

Can anyone answer my tension/friction question, please.

 

[stylez03]

Can you list the equations that's necessary? I'm not sure which equations you're talking about. Thank you

 

[marcusl]

The electric part of the Lorentz force, and Newton's second law.

 

[stylez03]

The electric part of the Lorentz force, and Newton's second law.

I'm no familiar with Lorentz force, the section we're in is introduction to Electricity and the only equation I've seen so far is Coulomb's Law.

F = k*|q1|*|q2| / r^2

If you could start me off with an equation that would be most helpful. I can't see where I have to go with the givens I have so far.

 

[marcusl]

The electric Lorentz force is
F=q*E
in SI units.

 

[stylez03]

So we have the particle traveling 0.45m in the first 3us and you said I had to find the average acceleration?

Velocity = 4.50m / 0.000003 seconds = 1.5*10^6 m/s

Now we have to take the avg. acceleration which should be the change in velocity divided by the change in time? Would that just be that solution divided by 3us again to obtain that value?

 

[marcusl]

You need to take a look in your book. The formula relating distance to acceleration and time is
x=0.5*a*t^2
Did you find it? Make sense?
Suggest you ask your teacher for some help.

 

[stylez03]

Makes sense, I just got it! Thanks again. It's been a very long time since I've done kinematics.