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**Need help with physics questions with charges and velocity!!!**

Hi,

I need some help with a couple problems from my AP physics class regarding charges and velocity.

1. Two insulating spheres having radii 0.41 cm and 0.61 cm, masses 016 kg and 0.78 kg and charges -2 micro coulombs and 4 micro coulombs are released from rest when their centers are separated by 0.5 meters. how fast is the smallest sphere moving when they collide. Answer in m/s.

i'm not quite sure how to tie in momentum to this question because you're given mass and need to find final velocity...but how do you connect the charges and radii into the problem? do you find the electrical force between the two..?

i have no idea how to solve it.

2.when a potential difference of 198V is applied to the plates of a parallel-plate capacitor the plates carry a surface charge density of 14nC/cm^2. The permittivity of a vacuum is 8.85419 10^-12 C^2/N*m^2. What is the spacing between the two plates? Answer in units of micrometers.

any help would be great.thanks!