Why do the lithospheric plates move?

What is the average speed of a car that travels 40 mph for 1 hour and 60 mph in another hour?

The man of mass m1 and the woman of mass m2 are standing on opposite ends of the platform of mass m0 which moves with negligible friction and is initially at rest with s = 0. the man and woman begin to approach each other. derive an expression for the displacement s of the platform when the two meet in terms of the displacement x1 of the man relative to the platform.

Is the portion of the electromagnetic spectrum that has a frequency just above that of visible light.