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(a) Two protons in a molecule are 3.90 10-10 m apart. Find the electric force exerted by one proton on the other.

magnitude:___________________N

direction: attractive or repulsive

________________________

(b) State how the magnitude of this force compares with the magnitude of the gravitational force exerted by one proton on the other.

Fe/Fg =_____________________

(c) What must be a particle's charge-to-mass ratio if the magnitude of the gravitational force between two of these particles is equal to the magnitude of electric force between them?

______________C/kg

Edit
Added Wed, 09 Dec '15
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a)

F=kq^2/d^2=1.52*10^-9 N

b)

you are comparing the ratio of the electric force to the gravitational force, which is given by the formula below:

F=Gm1*m2/r^2

where G is your gravitational constant which equals: 6.674*10^-11 N*m^2/kg^2

and m1 and m2 are the mass of the particles which are each: 1.673*10^-27kg

and r is once again 3.9*10-10 m.

The gravitational force is found to be: 1.228*10^-45 N

Now the ratio would just be your answer from Part A divided by 1.1228*10^-45 N,

which would result in 1.238*10^36 as the answer.

c)

you are finding the ratio of the charge to the mass, or q/m.

To do this set the equations for the gravitational force equal to the equation for the electric force as follows:

Fg=Fe

(G*m1m2)/r^2 = (ke*q1q2)/r^2

now move the variables around until you have a ratio of q/m,

hence:

(q/m)=(G/ke)^(1/2)

q/m = 8.616*10^-11

Edit
Added Wed, 09 Dec '15
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