Which of newton’s laws, when combined algebraically with his law of universal gravitation, can be used to calculate earth’s mass?
a) first
b) second
c) third

B) second law of motion which states that F=ma

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.