Sharon kicks a ball from the ground into the air with an upward velocity of 64 feet per second. The function h = -16t2 + 64t models the height h, in feet, of the ball at time t, in seconds. When will the ball reach the ground again?
Answer
A
1 second after the ball is thrown
B
2 seconds after the ball is thrown
C
3 seconds after the ball is thrown
D
4 seconds after the ball is thrown
Explanation
The ball is on the ground when its height is 0, so set −16t² + 64t = 0. Factoring gives −16t(t − 4) = 0, so t = 0 or t = 4. Since t = 0 is when Sharon kicks the ball, it reaches the ground again 4 seconds later: choice D.
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