
Arturo O. answered 06/22/16
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h(x) = -(1/2)(x-20)^2 +50
For h=0,
-(1/2)(x-20)^2 +50 = 0
x^2 - 40x + 400 - 100 = 0
x^2 - 40x + 300 = 0
x = (1/2){40±√{(40)^2 - 4(300)] = (1/2)(40±20) = 20±10 = 30 or 10
The ball is kicked up from the ground at x=10, then reaches the ground again at x=30, so its horizontal travel is 30-10=20