4. A baseball is hit at ground level, the ball is observed to reach its max height above ground level 3seconds after being hit. And 2.5seconds after reach this max height, the ball is observed to clear a fence of 97.5m. How high is the fence?

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- Oct 18th 2008, 08:34 PMyzc717I still dont get the last one?
4. A baseball is hit at ground level, the ball is observed to reach its max height above ground level 3seconds after being hit. And 2.5seconds after reach this max height, the ball is observed to clear a fence of 97.5m. How high is the fence?

- Oct 18th 2008, 09:13 PMTony2710
Using your intuition you should be able to work out if a problem is two dimensional or one dimensional.

All of the problems below are 2 dimensional because when the projection of the object is plotted, both the "y" and "x" co-ordinates are changing with time.

You should be able to solve these problems by using standard 2-d motion formula and substituting in the numbers to find the unknowns. - Oct 19th 2008, 02:13 PMyzc717
i got the previous three, still one left which I still dont get~

anyone can help me? - Oct 19th 2008, 10:08 PMTony2710
Hi,

Is the fence 97.5m away from where the ball was hit?

If so, then what you know is the following:

when t=3, y'=0.

when t=5.5, x=97.5.

What you need to find is the value of y when t=5.5, and x=97.5. - Oct 19th 2008, 11:03 PMtreetheta
$\displaystyle d = v_2 - 1/2at^2$

since $\displaystyle v_2 = 0 $ at 3 seconds

$\displaystyle d = -1/2a(2.5)^2$

where $\displaystyle a = 9.8m/s^2$ the acceleration due to gravity