Find a formula for the change in surface area of a uniform solid sphere of radius r if its coefficient of linear expansion is α (assumed constant) and its temperature is changed by δt.

i know the answer isδa = 8π r^2αδt [1+(1/2)αδt]

and that the problem involves linear expansion, but im not sure how to arrive at this equation. explain and show steps.

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.