Which of the following diagrams best represents the gravitational force W. the frictional force f, and the normal force N that act on the block?

It's D.

Weight always points downward.

The normal force always points perpendicular to the surface.

Friction opposes motion, so it points in the direction opposite the direction in which the block is moving.

the force on the thing and the distance the force moves the thing

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.