What best describes why the critical angle of an air-glass boundary is 39.3°? A. It is the angle of refraction in glass for which the angle of incidence in air is 90°. B. It is the angle of incidence in air for which the angle of refraction in glass is 90°. C. It is the angle of refraction in air for which the angle of incidence in glass is 90°. D. It is the angle of incidence in glass for which the angle of refraction in air is 90°.

Aperson gives a shopping cart an initial push along a horizontal floor to get it moving, and then lets go. the cart travels forward along the floor, gradually slowing as it moves. consider the horizontal force(s) on the cart while it is moving forward and slowing. which of the following statements is correct? (a) both a forward and a backward force are acting on the cart, but the forward force is larger. (b) only a forward force is acting which diminishes with time. (c) both a forward and a backward force are acting on the cart, but the backward force is larger. (d) only a backward force is acting, no forward force.