Heather hits a tennis ball upward with an initial speed of 32 feet per second. after how many seconds does the ball hit the ground? use the formula h = rt - 16t^2 where h represents height in feet and r represents the initial speed.

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h = 0 when the ball hit the ground, so 
0 = rt - 16t^2 
Since r = 32, 
0= 32t - 16t^2 
16t(2 - t) = 0 
t = 0 or 2 

At t=0, h=0 but the ball hasn't left the ground yet. 
Thus, the answer is 2.