Suppose the disk in the example has a hole cut out of it from its center, forming an annulus. The inner radius is r = 6.0 cm, and the outer radius is R = 15.0 cm. What is the potential (in V) of the disk at point P a distance of x = 23.0 cm from the center of the disk along the x-axis? The uniform surface charge density of the disk is 30 nC/m2.

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.

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.