6. A proton is released from rest 1.0 cm off a center of a uniformly charged disk of a 2.0 m radius carrying a +180 nC charge. What is the speed of the proton when it is 5 cm from the disk?

the speed of the proton  is  

Explanation:

Generally Electric potential energy resulting from a proton can be mathematically represented as

Where

        R is the radius of the disc which is given as

        q is the charge on the proton with  a value of  

        the mass of this proton has a value of  

        z is the distance of the center of the disk from the question

According the law of conservation of energy

  The change in kinetic energy of the proton + change in electrostatic   = 0            

                                                                              potential energy  

The change in kinetic energy is

Since u = 0 the equation becomes

change in electrostatic potential energy is

Substituting this into the equation we have

Recalling that   we have

         Substituting values        

Making v the subject

you have to draw the persons position over there

c. newton's third law of motion