Initial velocity and angle when a ball is kicked over a 3m fence

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SUMMARY

The discussion focuses on calculating the initial velocity and launch angle required for a ball to clear a 3-meter fence. The equations of motion used include horizontal and vertical components, specifically \(x = x_0 + v_{0,x}t\) and \(y = y_0 + v_{0,y}t - \frac{1}{2}gt^2\). The correct angle derived from the calculations is approximately \(58.3^\circ\) with an initial velocity of \(9.76 \, \text{m/s}\), contradicting the common assumption that \(45^\circ\) is optimal for maximum range. The discussion highlights the importance of verifying assumptions in physics problems.

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  • Basic calculus for optimization techniques
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  • #61
kuruman said:
This completes the condition for optimizing one of ##\Delta x##, ##\Delta y## or ##v_0## as the projection angle is varied:

"At optimization,(a) the projection velocity and the velocity at target are perpendicular and (b) the transit time is the same as if the projectile were dropped from rest a distance equal to the magnitude of the overall displacement vector."

I am amazed that there is still juice left to squeeze out of projectile motion.
👍 See also Winans Equations 20 - 27.
 
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  • #62
Instead of being amazed I should have reread Winans. Nevertheless, I think it's good to bring forth this simple statement of trajectory optimization. It is more likely to be noticed here than in a 1961 AJP article.
 
  • #63
kuruman said:
Instead of being amazed I should have reread Winans. Nevertheless, I think it's good to bring forth this simple statement of trajectory optimization. It is more likely to be noticed here than in a 1961 AJP article.
It most definitely is. Not to mention ##\vec{a}\times \vec{s} = \vec{v} \times \vec{u}## which I 'punt' whenever I can!
 
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