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Old Sep 15th 2009, 05:42 PM   #1
Join Date: Sep 2009
Posts: 32
Another Hard Physics Question now with attempt

A placekicker must kick a football from a point 36.0 m (about 39.0 yd) from the goal, and the ball must clear the crossbar, which is 3.05 m high. When kicked, the ball leaves the ground with a velocity of 21.2 m/s at an angle of 45.0 to the horizontal.
By how much does the ball clear or fall short of clearing the crossbar?

Any help is appreciated. Thanks so much.

Well, first I found out that the ball does clear the crossbar. . . but I am trying to once again do the components with the angles and finding the hypotenuse of the vectors. But, this might be completely wrong. Help please?

Last edited by rjsci13; Sep 15th 2009 at 06:17 PM.
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Old Sep 16th 2009, 12:08 AM   #2
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resolve the velocity into its components and then treat them independently.

The cos component will give you the horizontal velocity.

The distance to the post divided by this will give you the time available for the ball before it reaches the post.

Use this time in $\displaystyle s\ =\ u\ t\ +\ \frac{1}{2}\ g\ t^2$. for the vertical motion and remember g = - 9.8 and u = sin component of velocity.

If this s < 3.05 it does not clear and vice-versa.
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