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

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The discussion revolves around calculating the initial velocity and angle required for a ball to clear a 3m fence. The user attempts to derive the correct angle and velocity using projectile motion equations but consistently arrives at incorrect results, particularly questioning why 45 degrees is deemed wrong. Other participants clarify that the angle must be optimized to minimize the initial velocity while ensuring the ball clears the fence, suggesting that the user's approach may have overlooked this optimization aspect. The conversation highlights the importance of correctly applying the physics principles and equations involved in projectile motion, particularly in relation to the angle of launch and the conditions for minimum velocity. Ultimately, the user is encouraged to reassess their calculations and consider the optimization techniques discussed.
  • #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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