Which of these is not an event that make the moon as it is today?
a. iron sank into earth's core.
b. plate tectonics caused lava to flow.
c. earth and a planetesimal collided.
d. the lunar surface melted and was bombarded by meteoroids

(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.)