Electric filed physics problem. Help

[TSny]

Hint: Write U as U = 1/2 (CV) V and recall that CV = Q for a capacitor. So, you can express U in terms of Q and V (which you have already calculated) and you won't need a value for C.

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

 

[vela]

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

 

[sept26bc]

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

 

[vela]

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.

 

[sept26bc]

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

 

[sept26bc]

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?

 

[SammyS]

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 \displaystyle \frac{|F_\text{electric}|}{|F_\text{gravity}|}=1\ . Correct?

How is \displaystyle |F_\text{electric}| related to E and \displaystyle |F_\text{gravity}| related to g ?

 

[sept26bc]

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

 

[SammyS]

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

If the particle hovers, what is its acceleration?

 

[sept26bc]

the acceleration would be zero because its not moving.

 

[vela]

So you know there are two forces on the particle, the force of gravity $\vec{F}_g$ and the electric force $\vec{F}_E$. You also know the acceleration is 0 because it's not moving.

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?