Question

Little hand on this problem

Answer 1

So here where I'm
\(a=\frac{eE}{m}\)

Answer 2

I found the acceleration of the electron

Answer 3

I need the distance x just before it will strike the plate b

Answer 4

Yeah what does closest approach mean? I never ran into a phrase like that before

Answer 5

I'm thinking of kinematic of course here
x=v0t+a/2 t^2

Answer 6

that is just a weird wording that means the distance before it strikes the plate B

Answer 7

and we want that to be the closet one

Answer 8

@phi

Answer 9

what I'm not paying attention to here?

Answer 10

I must be misunderstanding something here. Does the electron reach a peak proximity to plate B?

Answer 11

we could find t when it strikes the plate B but that won;t be helpful

Answer 12

what do you mean by peak proximity?
if you mean does it reach B yes it does

Answer 13

we can find velocity at B and time as well

Answer 14

distance we know 40 mm

Answer 15

it reads like the electron is decelerating?

Answer 16

no it should accelerate due the electric field

Answer 17

then the question does not make sense (to me)

Answer 18

we put the electron and it start moving from v0=10^7 m/s

Answer 19

may be i'm understanding the problem the wrong way? I'm not sure

Answer 20

if it accelerates into the plate, then 0 is the answer
(it hits the plate)
so I'm guessing the field works against the electron or makes it curve (though I'm probably thinking of a magnetic field in the latter case)

Answer 21

the answer is 16 mm

Answer 22

so definitely it is not zero

Answer 23

zero is from where it starts

Answer 24

I agree with Phi, that's also why I am not understanding

Answer 25

Unless the electric field was a magnetic field, or if it caused the electron to decelerate, the electron will hit plate B. And that gives an answer of 0

Answer 26

even if it is a deceleration that does not solve the issue still

Answer 27

indeed looking back it is a deceleration

Answer 28

closest to b the kinetic energy=0

Answer 29

i think i got it

Answer 30

solution:
At point C close to B v=0
v^2=v0^2-2ax
x=v0^2/2a
x=23.7 mm
d=40-23.7=16.3
which is the desired answer
thanks guys for your input

Answer 31

it was the about understanding the question after all
as you said it is a deceleration

Answer 32

@phi thanks