Rob and his sister joan are standing on their apartment balcony. rob throws a ball straight out from the balcony. at the same time, joan drops a ball straight down. both balls reach the ground at the same time. which factor causes the two balls to reach the ground at the same time?

The initial vertical velocities of the balls are the same.

Explanation:

If the air resistance is despised, the phenomena can be expressed by the equation for an accelerated retiling movement:

H = v0*t + gt²/2

Where v0 is the initial velocity, g is the gravity acceleration, and t the time. So, if Rob and Joan drop the ball at the same time and they reach the ground at the same time, the initial vertical velocity of the balls must be the same.

i just learnt this recently but i need to look through my notes again