The drawing shows three materials, a, b, and c. a ray of light strikes the a−b interface at an angle that just barely exceeds its critical angle of 40.0°. the reflected ray then strikes the a−c interface at an angle of incidence that just barely exceeds its critical angle (which is not 40.0°). the index of refraction of material a is na = 1.71. find the indices of refraction for the two other materials. nb = ?
nc = ?

Is a  vector quantity  that refers to "the rate at which an object changes its position." imagine a person moving rapidly - one step forward and one step back - always returning to the original starting position. while this might result in a frenzy of activity, it would result in a zero velocity. because the person always returns to the original position, the motion would never result in a change in position. since velocity is defined as the rate at which the position changes, this motion results in zero velocity. if a person in motion wishes to maximize their velocity, then that person must make every effort to maximize the amount that they are displaced from their original position. every step must go into moving that person further from where he or she started. for certain, the person should never change directions and begin to return to the starting position.

Multiply the 3 dimensions, assuming it is a rectangular cuboid, to get the volume in cm³ divide mass by volume to get density in g/cm³