Calculating Initial Velocity for Symmetric Projectile Motion

AI Thread Summary
The discussion focuses on calculating the initial velocity for a symmetric projectile motion problem involving a potato launched through a wall opening. Participants emphasize the importance of kinematic equations and the concept of maximum height and time to reach it. A key point is the "reversibility" of projectile motion, allowing the trajectory to be analyzed in reverse to determine the necessary launch conditions. Simplifying the problem by adjusting the height and aligning the axis with the launch point is suggested as a helpful approach. Overall, the conversation revolves around breaking down the problem into manageable components to find the required initial velocity.
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Homework Statement

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Homework Equations

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The Attempt at a Solution



I have tried, but I honestly have no Idea how to start this problem.
 

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Start by listing kinematic equations that might be useful. What's the maximum height of a launched projectile? How much time does it take to reach its maximum height?

The problem doesn't explicitly say what height the potato may have when it passes over the screen, so I suppose that you could assume that it just clears it at the screen's height.

Hint: can you find the equation for the trajectory of a "reverse" potato launched from the center of the wall opening and just clearing the screen?
 
I am a bit confused about your hint. a reverse? what is that exactly mean like wouldn't it need a velocity to go from the hole in the wall to the top of the screen?
 
doc2142 said:
I am a bit confused about your hint. a reverse? what is that exactly mean like wouldn't it need a velocity to go from the hole in the wall to the top of the screen?

Yup. One property of projectile motion is that its trajectories are "reversible". You can launch a projectile and plot its trajectory to its landing point, and if you note its landing angle and speed, you can launch it from there back along its trajectory by using the same speed and angle to do so.

So what velocity (x and y components) would take a potato from the center of the window to the top of the screen as the trajectory apex?
 
Could you simplify this somewhat by removing 10cm of height from everything, setting your axis inline with where the projectile begins? Then perhaps consider the system as symmetric about the screen?
 
JHamm said:
Could you simplify this somewhat by removing 10cm of height from everything, setting your axis inline with where the projectile begins? Then perhaps consider the system as symmetric about the screen?

Yes! Those are two easy simplifications that hardly require any elbow grease to carry out :smile:
 

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