Particle Motion in Homogenous Gravitational and Electrical Fields

[Kostas Tzim]

Homework Statement

http://prntscr.com/6d250v Hello, ignore the greek language. It says that this particle is in a homogenous gravitational and electrical field (from left to right the letters are a,b,c,d,e)

Homework Equations

the question is: Which is the most likely route it'll follow?

The Attempt at a Solution

i cannot understand why it cannot be the b.), I suppose its due to the gravity and the Force cause they stay constant thus it won't move in a parabolic orbit but in a straight line..However i learned that in a electrical field between 2 bars where we ignore the gravitational field the particle moves in a parabolic way...i think I am missing something...

 

[sk1105]

If the particle is subatomic, I would have thought you would be permitted to ignore the gravitational force, since this is absolutely tiny. However, all the options have a downward component, so I guess not. The left/right direction depends on the charge of the particle, and remember that gravity and the E field will both cause an acceleration through Newton's second law. But one is (much) stronger than the other, so think about how that would affect the shape.

 

[Kostas Tzim]

It's my mistake i didnt mention. The particle has negative charge. I suppose that it's an electron..The answer says its C ( γ) in the picture

 

[Kostas Tzim]

anyone? :)

 

[PeroK]

What can you say about each of the gravitational and electrical accelerations? Given that the fields are homogeneous.

 

[Kostas Tzim]

they are constant?

 

[PeroK]

Yes. Can you write the equations for the x and y displacements? Assuming acceleration g in the y direction and a in the x-direction?

 

[Kostas Tzim]

Assuming the particle has no initial velocity. $y=\dfrac{1}{2}gt^2$ and $x=\dfrac{1}{2}at^2$ where from the $F=E|q|$ $<=>$$a=\dfrac{E|q|}{m}$

 

[PeroK]

Why are the equations different? $t^2$ in one and $t$ in another?

 

[Kostas Tzim]

sorry i didnt notice i was thinking about velocity

 

[PeroK]

Okay. Now plot x against y on a graph.

 

[Kostas Tzim]

if i did this right in a straight line where it starts from the beginning of the axes

 

[PeroK]

It would be a straight line, yes.

 

[Kostas Tzim]

i got it now :) thank you very much for your time