Which of the following describes the formation of air convection currents?

a. molecules in cooler air move faster and farther apart than those in warmer air.
b. cooler air moves in over the warm air and pushes it down.
c. the sun warms the land, which heats the air above it.
d. all of the above

Aspring has a relaxed length of 33 cm (0.33 m) and its spring stiffness is 6 n/m. you glue a 76 gram block (0.076 kg) to the top of the spring, and push the block down, compressing the spring so its total length is 15 cm. you make sure the block is at rest, then at time t=0 you quickly move your hand away. the block begins to move upward, because the upward force on the block by the spring is greater than the downward force on the block by the earth. calculate y vs. time for the block during a 0.09-second interval after you release the block, by applying the momentum principle in three steps each of 0.03-second duration.