The speed of a tennis ball on the return of a serve can be just as fast as the serve, even though the racket
isn't swung very fast. How can this be?

It is increased due to the doppler effect. (apex)

Ray 2 should cross through the focal point on the right side of the lens.

Hi. i believe this is called a scientific  theory.cheers!

Gravity, from the center of mass of the box, extending downward normal force, from the floor under the box, extending upward, equal to gravity push force, acting at a point on the box, extending in the direction of motion friction, acting at any point on the box directly opposite the push, extending directly opposite to the motion