Select the statement that is true regarding scientific theories. a. scientific theories are what laws are called before they are proven. b. scientific theories attempt to explain why natural events occur. c. scientific theories are based on true facts. d. scientific theories describe natural events.

What would the difference of spectral lines emitted by hydrogen gas in distant galaxies which is normally found at a wavelength of 21 cm on earth, be observed at 21.1 centimeters?

Atrain departs from its station at a constant acceleration of 5 m/s. what is the speed of the train at the end of 20s?

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.