(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

2. Relevant equations

Fq=E*q

kinematics equations...

3. The attempt at a solution

The problem is that in the end I get a value ABOVE the mid-axis instead of below. I don't know what I'm doing wrong. Please check my reasoning.

Stage 1: While it's in between the plates where there is an electric field...

1. Find Fq (electrostatic force). Fq=E*q=2.8*10^{4}*1.6*10^{-19}=4.48*10^{-15}N [up]

2. Find Fg (force due to gravity). Fg=9.1*10^{-31}*9.8=8.92*10^{-30}N [down]

3. Find Fnet acting on the electron and its vertical acceleration. Fnet=4.48*10^{-15}N [up] - 8.92*10^{-30}N = 4.48*10^{-15}[up]. Now find acceleration. Fnet=ma. a= 4.92*10^{15}m/s2 [up]

4. Find its vertical displacement from beginning up to the end of the plates. d=v_{i}t+1/2at^{2}. t=0.05m/2.7*10^7m/s = 1.9*10^{-9}s. and sub the time found into the displacement equation, i get d=0.0089m up.

Stage 2: After it leaves the plates and enter the area where there is no electric field.

1. Find final velocity (near the end of the plates and at point where it is JUST about to enter the part without the plates). V2=V1+at=0+(4.92*10^{15}m/s^{2})(1.9*10^{-9})=9,348,000m/s [up]

2. Find vertical displacement. This time only gravity is acting on it since there is no electric field to pull the electron "up". Time is found by dividing distance by horizontal velocity which is constant. so 0.015m/2.7*10^{7}=5.6*10^{-9}s.

d=V1t+1/2at2

d=9.348*10^{6}(5.6*10^{-9})+1/2(-9.8)(5.6*10^{-9})

^{2}

d=0.0523m up

total displacement = 0.0523m + 0.0089m = 0.06m above the horizontal axis. What's wrong?

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# Homework Help: Electrostatics problem (electron's motion in cathode ray tube)

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