Vince is determined to test law of gravity for himself walks a skyscraper 900ft. with zero initial velocity.
Five seconds later, superman arrives at the scene and drive off the roof to save Vince.
1. what must be the initial velocity of superman to catch Vince just before Vince reach the ground?
2. what must be the height of skyscraper so that even superman cannot save Vince when came in five seconds later?