College Physics
posted by Marcus .
A proton is put on the positive Y axis a large distance (100km) from the origin. What is the minimum speed required in the  Y direction so the proton will just reach the point (0,20) cm?

Is there some sort of repelling positive charge at the origin or what ?
If so the kinetic energy at infinity has to equal the potential energy at 20 cm 
0,0 is the origin there is no repelling charge

Then there is no force on the proton and it will keep going forever with infintesimal velocity.

So what's the minimum speed ?