Focus of parabola, checking my answer.

1. Mar 4, 2012

jkristia

I just had this question in an online test I took, and first I had 16ft, but for some unknown reason I chose to change it to 64ft right before I submitted the test, and of course I got it wrong. So I just want to confirm the answer is indeed 16ft.

1. The problem statement, all variables and given/known data

A parabolic antenna has a diameter of 32 feet and is 4 foot deep. How far is the focus from the vertex?

2. Relevant equations

3. The attempt at a solution

My answer - Focus for this parabola is (0, a), so (0, 16) or 16ft from vertex

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2. Mar 4, 2012

LCKurtz

I think you have the depth and the diameter reversed.

3. Mar 4, 2012

jkristia

Hmm, not sure I understand why you think that.

The way I read this is when x = 16, then y = 4, (the 'depth' 16 feet out to the bottom of the vertext is 4 feet), but maybe I misunderstood something.

4. Mar 4, 2012

LCKurtz

Never mind. I had my two variables interchanged. You are correct.