Andrew is stopped at the top of a hill and then begins coasting down the hill on his skateboard. After 5.2 seconds he reaches a speed of 6.5 m/s. What is Andrew's average acceleration?

In a closed system, the total energy prior to an energy transformation is the total energy after. a. equal to b. unrelated to c. greater than d. less than

Light from the sun reaches the earth in 8.3 minutes. the velocity is 3.00 x 10^8 m/s. how far is earth from the sun? i know how to get to d = (3 x 10^8 m/s)(498 sec). i just don't know how to get from there to the answer being 1.5 x 10^11 m.

This is the substance(s) formed in a chemical reaction.