# Physics

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I'm having trouble relating Work, with Electric Field, with Kinematics. The question is asking:

How fast and what direction is the particle moving, given:

Disk: radius = 0.1m, surface charge density = 3.7mC/m2

Particle: 4.5 mC, mass = 75 mg accelerates from a point perpednicular from the center of the disk, with a final speed = 1.0 m/s

Work done on particle is -3 mJ

I think my main obstacle is finding the change in distance of the particle when I try to relate these variables.

Any help is appreciated, thank you.

• Physics -

It is not clear what they are asking for. Does the particle start with zero velocity? You ask for a final velocity and yet they tell you what the final speed is. The velocity direction will remain along the axis, if it started out that way.

The E field will be uniform as the charge moves the first 0.03 m away from the surface , and then vary with 1/x^2 as the distance from the surface exceeds 0.3 m.

The negative work done on the particle means there is an attractive force to the plate, so it is always slowing down.