Solve Proton Homework: Min Speed to Miss Lower Plate

[Vanessa Avila]

Homework Statement

In the figure, a proton, mass 1.67×10^−27 kg, is projected horizontally midway between two parallel plates that are separated by 0.20cm, with an electrical field with magnitude 7.8×10^5N/C between the plates. If the plates are 5.40cm long, find the minimum speed of the proton that just misses the lower plate as it emerges from the field.

Homework Equations

q(E) = ma
x = vt
y = 1/2a(t^2)

The Attempt at a Solution

[/B]
This is what I did:
1.6*10^-19(7.8*10^5) = 1.67*10^-27 (a)
solving for a I get: 7.47*10^13 m/s^2

then i solve for t
2*10^-3 = (1/2)(7.47*10^13)(t^2)
t = sqrt(7.47*10^13/((2)(2*10^-3))
I get 7.32*10^-9 s

then i plug that in the x = vt eqn
0.054/7.23*10^-9 = v
v = 7.4*10^6 m/s

But that is wrong

 

[Xiaochao Zheng]

It says the proton comes in midway, which means y is 0.1cm, not 0.2cm

 

[Vanessa Avila]

It says the proton comes in midway, which means y is 0.1cm, not 0.2cm

Oh I see.Thank you!