- #1

Leeoku

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## Homework Statement

An electron is projected at an angle of 30.8° above the horizontal at a speed of 8.20×105 m/s in a region where the electric field is E = 388j N/C. Neglecting the effects of gravity, calculate the time it takes the electron to return to its initial height.

Answer: 1.23e-08 s

## Homework Equations

v = v_0+at

F = qE = MA

## The Attempt at a Solution

Components of Velocity

V_x = Vcos30.8

V_y = Vsin30.8

F = qE = ma

a = qE/m

= 1.6e-19*388/9.11e-31

= 6.81e13

V = v_0+at (set V = 0 because max height)

0 = v_y+at

t = 6.17e-9

Now i was playing with nums and found that if i multiplied V_y by 2 then divided it by a that is the right answer, why?