good one

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Re: good one

by sudhir3127 » Tue Dec 02, 2008 7:56 am
bacali wrote:OA: B
it will reach the max height when t =3
2 seconds later means 5 seconds

-16( 5-3)^2 + 150 = 86

hope its clear..

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by bacali » Tue Dec 02, 2008 7:57 am
Its not 8 AM yet so kinda slow right now. Thanks.

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Re: good one

by hwiya320 » Tue Dec 02, 2008 10:18 am
sudhir3127 wrote:
bacali wrote:OA: B
it will reach the max height when t =3
2 seconds later means 5 seconds

-16( 5-3)^2 + 150 = 86

hope its clear..
how did you calculate that maxiumum height is 3? is it because that's when h is the highest? since -16 x time is negative?

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by sudipto » Wed Dec 03, 2008 3:01 am
The only way I could see to determine the time it reaches max height is to take the derivative of h and set dh/dt = 0

dh/dt = -32 (t-3) = 0 => t =3

But I'm sure this is not expected in GMAT. Thoughts ??

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Re: good one

by orel » Wed Dec 03, 2008 6:38 am
hwiya320 wrote:
sudhir3127 wrote:
bacali wrote:OA: B
it will reach the max height when t =3
2 seconds later means 5 seconds

-16( 5-3)^2 + 150 = 86

hope its clear..
how did you calculate that maxiumum height is 3? is it because that's when h is the highest? since -16 x time is negative?
The Max height is reached when the given formula reaches its max value for H, that is when t=3.

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by niraj_a » Wed Dec 03, 2008 11:45 am
true, i started with this thought - if GMAT asks you to max something, then you to have min/reduce something else.

so in this case, since we have to find H, any value of T below 0 would be detrimental to our goal.