An unknown force decelerates a crate of mass 20 kg from 30 m/s to 0. If the distance the force acts over is 10 meters, what is the force?

1) when you rub your hands together quickly, the kinetic energy is converted to mechanical energy.2) thermal energy from the sun travels to earth as infrared waves.3) energy is transferred through the matter of space by electromagnetic waves. 4) when a match is burned, chemical potential energy is converted to thermal and radiant energy. 5) seismicwaves are caused by back and forth movement , or vibration, of an object. 6) mechanicalenergy in an engine changes thermal energy into kinetic energy to make a car move.

  concave means having an outline or surface that curves inward like the interior of a circle or sphere. so the mirror curves inward.