A small metal ball is given a negative charge, then brought near (i. e., within about 1/10 the length of the rod) to end A of the rod. What happens to end A of the rod when the ball approaches it closely this first time?

If the rod is a conductor, the electrons are free to move within. So when the negative charge is brought towards the rod, the negatively charged electrons near the ball are repelled away towards the other end of the rod, leaving a net positive charge on the end of the rod near the ball. This causes the rod to be attracted towards the negatively charged ball and move closer.

Explanation:

c.the charges if the proton and electron and gravity

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.