- #26

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F= ma and E=F/q So i sub, and get ma= Eq then solved for q/m

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- Thread starter sept26bc
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- #26

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F= ma and E=F/q So i sub, and get ma= Eq then solved for q/m

- #27

TSny

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Can you explain your steps in getting from ma = Eq to the result for q/m?

- #28

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- #29

TSny

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ok except for the location of the decimal point and you need to include proper units with your answer.

- #30

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okay if that is correct how would I find the total energy associated with the electric field of the Earth, if Earth is a charged capacitor? Would I use U=1/2 CV^2. Does the value of capacitance of the Earth matter?

- #31

TSny

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Or, you could use Q = CV to find C and then plug into your equation.

- #32

vela

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Hint: If you want to find the acceleration, you use Newton's second law.

- #33

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Okay Thanks! I found acceleration can you reassure my answer?

so F=ma and E=F/q I substitute and get a= Eq/m and with the numbers plugged in I get:

a= (-150N/C)(1.602*10^-19 Nm^2/C^2) / (1.67*10^-27 kg)

a= -1.44*10^10 m/s^2

for charge to mass ratio I used E=ma/q rearrange to get q/m= a/E. Plug in the numbers of a and E, (-1.44*10^10m/s^2)/ (-150N/C) = q/m answer is -0.0654 kq/C

Another question is how would I find the total energy associated with electrical field of the Earth if the Earth is like a charged capacitor? Would I use U=1/2CV^2 ?

thanks

- #34

vela

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You didn't do part 4 correctly. What are the forces on the particle and what is its acceleration if it's hovering?

If you're considering the Earth a capacitor, then yes, you can use that formula. You'll need to figure out the capacitance of the Earth.

- #35

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I don't understand the hovering part, would it be the gravitational force 9.81? what would I do then?

- #36

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Vela. I'm really confused I've been working on this for hours. I know that the gravitational and electric force have to cancel in order for the particle to be hovering.how would another force be included in the equation q/m=a/E ? or am i using the wrong equation?

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- #37

SammyS

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Vela. I'm really confused I've been working on this for hours. I know that the gravitational and electric force have to cancel in order for the particle to be hovering.how would another force be included in the equation q/m=a/E ? or am i using the wrong equation?

So, you need [itex]\displaystyle \frac{|F_\text{electric}|}{|F_\text{gravity}|}=1\ .[/itex] Correct?

How is [itex]\displaystyle |F_\text{electric}| [/itex] related to

- #38

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well F=ma and E=F/q so E= ma/q

|Felectric| is related to E by E=F/q

and |Fgravity| related to g by F=ma

correct?

im not understanding why you have Felectric/ Fgravity=1

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- #39

SammyS

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If the particle hovers, what is its acceleration?well F=ma and E=F/q so E= ma/q

|Felectric| is related to E by E=F/q

and |Fgravity| related to g by F=ma

correct?

im not understanding why you have Felectric/ Fgravity=1

- #40

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the acceleration would be zero because its not moving.

- #41

vela

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What is the magnitude of ##\vec{F}_g##? What is the magnitude of ##\vec{F}_E##?

Now take all that info and use Newton's second law, which is ##\sum \vec{F} = ma##. What do you get?

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