To solve this problem you must apply the proccedure shown below:
1- You have the following information give in the problem above:
- The ball is thrown downward from the top of a 190-foot building with an initial velocity of 21 feet per second.
- The height of the ball h after t seconds is given by this equation: h=-16t²-21t+190.
2- h=0 when the ball strikes the ground, then you have:
-16t²-21t+190=0
3. When you solve the quadratic equation shown above, you obtain:
t=2.85 seconds
The answer is: 2.85 seconds.
