Select the correct expression that gives the block's acceleration at a displacement x from the equilibrium position. Note that x can be either positive or negative; that is, the block can be either to the right or left of its equilibrium position.
a. a=−kx
b. a=kx
c. a=kmx
d. a=−kmx

Agroup of students were investigating the force of gravity. they began by dropping a foam ball from a height of 3 meters into a bucket of sand. the ball hit the sand in 0.306 seconds. they dropped additional balls of approximately the same diameter, but of different masses. here is the data they collected. based on this experiment and the collected data, what would their conclusion be?