Which type of wave can travel without a medium

(a) assume the equation x = at^3 + bt describes the motion of a particular object, with x having the dimension of length and t having the dimension of time. determine the dimensions of the constants a and b. (use the following as necessary: l and t, where l is the unit of length and t is the unit of time.) (b) determine the dimensions of the derivative dx/dt = 3at^2 + b. (use the following as necessary: l and t, where l is the unit of length and t is the unit of time.)

In which of these cases are the two wave points considered to be in phase with each other?

Which of the following are molecules? a. al b. ag c. mgcl2 d. nacl e. c3h8