A beach ball(30g) and a sponge ball(30g) dropped off a 100m tower, which hits the ground first? Why?

In real life, air resistance decreases the velocity of a falling object. The feather and water melon will accelerate at the same rate in a vacuum. But real life has no vacuum.

Steve is correct.

As the velocity increases, the upward force of air resistance increases. The force pushes up on the surface which is facing downward.

The shape and texture of the surface also affect the total force.

A beach ball is spherical and smooth.

A sponge ball is spherical and not as smooth as the beach ball.

The air resistance of the sponge ball is greater than the air resistance of the beach ball.

So, the beach ball will hit the ground first!

Since you didn't tell me, I'm assuming the beach ball is larger in size than the sponge ball.

The balls have equal downward force applied bu gravity. Fd = m*g

They each reach their terminal velocity shortly after being dropped. The beach ball has a much lower Vt than the sponge ball because of its superior size. Ergo, the time to fall 100 m is given approximately by

t = 100/Vt from which it is clear that the lower Vt, the longer the time to fall. The sponge ball hits first.

They hit at the same time. Why you ask? Science.

they hit the ground at the same time.

same idea with the watermelon and feather.