Physics Help Forum Another Hard Physics Question

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Sep 15th 2009, 04:42 PM #1 Member   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 05:17 PM.
 Sep 15th 2009, 11:08 PM #2 Physics Team   Join Date: Feb 2009 Posts: 1,425 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.

 Tags hard, physics, question

 Thread Tools Display Modes Linear Mode

 Similar Physics Forum Discussions Thread Thread Starter Forum Replies Last Post Ace Electricity and Magnetism 3 Feb 6th 2010 11:07 AM BearN Advanced Thermodynamics 0 Sep 22nd 2009 12:36 PM KaylaN Kinematics and Dynamics 1 Sep 22nd 2009 03:55 AM oblixps Kinematics and Dynamics 6 Sep 10th 2009 10:38 PM Inertialforce Advanced Electricity and Magnetism 1 Jan 7th 2009 05:20 PM