Arock is thrown downward from an unknown height above the ground with an initial speed of 21m/s. it strikes the ground 8s later. determine the initial height of the rock above the ground. the acceleration of gravity is 9m/s/s. answer in units of m

In what direction does the medium move relative to the direction of the wave? explain.

Select all the correct answers. which three statements about electromagnetic radiation are true?

Beryl states that insulation with the smallest possible thermal conductivity is best to keep a house warm in winter, but worst for keeping a house cool in summer. sapphire insists the reverse is true: low thermal conductivity is good in the summer, but bad in the winter. which one, if either is correct? a. beryl, because low thermal conductivity results in low heat transfer. b. beryl, because low thermal conductivity results in high heat transfer. d. sapphire, because low thermal conductivity results in high heat transfer. e. neither, because low heat transfer is desirable both in summer and in winter.