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-   -   Help me figure out where this equation was derived (http://www.physicsforums.com/showthread.php?t=373033)

d3111 Jan27-10 12:21 AM

Help me figure out where this equation was derived
 
1. The problem statement, all variables and given/known data

A placekicker must kick a football from a point 36.0 m (about 40 yards) from the goal, and half the crowd hopes the ball will clear the crossbar, which is 3.05 m high. When kicked, the ball leaves the ground with a speed of 23.0 m/s at an angle of 46.0 to the horizontal.

I have completed the problem correctly but was told to find time by t= delta x / (vi *costheta)

Where is this equation derived from is what i'm asking?

thanks

Mentallic Jan27-10 01:08 AM

Re: Help me figure out where this equation was derived
 
The time (t) it takes for something with uniform speed (u) to complete some displacement ([itex]\Delta x[/itex]) is given by [tex]t=\frac{\Delta x}{u}[/tex]. But the problem is that the uniform speed isn't quite the initial velocity of the ball. The ball is projected at an angle to the horizontal, so can you figure out what the horizontal velocity of the ball is?


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