# Kinetic Energy

by elizabethrae
Tags: energy, kinetic
 P: 3 1. The problem statement, all variables and given/known data In an electron microscope, there is an electron gun that contains two charged metallic plates 2.75 cm apart. An electric force accelerates each electron in the beam from rest to 8.90% of the speed of light over this distance. (Ignore the effects of relativity in your calculations.) (a) Determine the kinetic energy of the electron as it leaves the electron gun. Electrons carry this energy to a phosphorescent viewing screen where the microscope's image is formed, making it glow. (b) For an electron passing between the plates in the electron gun, determine the magnitude of the constant electric force acting on the electron. (c) Determine the acceleration of the electron. (d) Determine the time interval the electron spends between the plates. 3. The attempt at a solution So I know you can find kinetic energy with the equation k=1/2mv[SUP]2[SUP] but what would I use for the mass? I assume you would just have to calculate out the velocity from the percentage of the speed of light correct? I have no idea what to do for b) and d). And for c) I assume you would do delta velocity over delta time but what would the time be? Thank You! 1. The problem statement, all variables and given/known data 2. Relevant equations 3. The attempt at a solution
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P: 12,069
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 Quote by elizabethrae So I know you can find kinetic energy with the equation k=1/2mv[SUP]2[SUP] but what would I use for the mass?
Since the particles in the problem are electrons, use the mass of an electron.
 I assume you would just have to calculate out the velocity from the percentage of the speed of light correct?
Yes, correct.
 I have no idea what to do for b) and d).
For (b), you could use the fact that the energy gain of an electron equals the work done by the electric field. There is also a formula that relates work done to the force applied to an object.
 And for c) I assume you would do delta velocity over delta time but what would the time be?
You don't have to do that, there are other equations that involve acceleration and do not involve time.

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