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A ball is thrown in the air from a ledge. Its height in feet is represented by f(x) = –16(x2 – 5x – 6), where x is the number of seconds since the ball has been thrown. The height of the ball is 0 feet when it hits the ground. How many seconds does it take the ball to reach the ground?

User Web Worm
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2 Answers

4 votes

six seconds (apex) :)

User Prine
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7 votes

The ball takes 6 seconds to reach the ground.

Step-by-step explanation

Height of the ball after
x seconds is represented by....


f(x)= -16(x^2 -5x-6)

The height of the ball is 0 feet when it hits the ground. So, for finding the number of second the ball takes to reach the ground, we will just plug
f(x)=0 into the above equation and then solve for
x.

Thus...


0=-16(x^2-5x-6)\\ \\ x^2-5x-6=0\\ \\ (x-6)(x+1)=0

Using zero-product property....


x-6=0\\ x=6

and


x+1=0\\ x=-1 (Negative value is ignored as time can't be negative)

So, the ball takes 6 seconds to reach the ground.

User Reema
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8.6k points
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