# Parabola Word Problem

• Jun 14th 2009, 05:47 PM
Parabola Word Problem
Mary is playing golf. The diagram below describes her situation. Determine the equation of this relation. Then find the time when the ball is 20m away from the hole.

What I did so far was the following:

Find a using P(0, 15) and s = -50, t = 50 into y=a(x-s)(x-t).

15 = a(0-(-50))(0-50)
15 = a(50)(-50)
15 = 2500a
3/500 = a

Therefore the equation of this relation is y = 3/500(x+50)(x-50)

Now the problem is, I'm not sure how to find the time. Do I substitute 20m into the above equation? Also, what units would the time be in?
• Jun 14th 2009, 08:51 PM
apcalculus
Quote:

Mary is playing golf. The diagram below describes her situation. Determine the equation of this relation. Then find the time when the ball is 20m away from the hole.

What I did so far was the following:

Find a using P(0, 15) and s = -50, t = 50 into y=a(x-s)(x-t).

15 = a(0-(-50))(0-50)
15 = a(50)(-50)
15 = 2500a
3/500 = a

Therefore the equation of this relation is y = 3/500(x+50)(x-50)

Now the problem is, I'm not sure how to find the time. Do I substitute 20m into the above equation? Also, what units would the time be in?

20 meters from the hole means that it is 30 meters from the origin. so you plug in either x=30 or x=-30, depending on which end the hole is. but the answer should be the same here (the y-coordinates are equal at x=30 and x=-30).

Good luck!!
• Jun 14th 2009, 08:52 PM
yeongil
EDIT: apcalculus answered my question. (Doh)

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