Simple Projectile Motion Problem. Unknown initial speed.

AI Thread Summary
A ball is launched at an angle of 30 degrees with an unknown initial speed, aiming to land 3 meters away at a height of 0 meters. One participant calculated the required speed to be 5.829 m/s but expressed uncertainty about the accuracy of this result. The discussion emphasizes the importance of verifying calculations using kinematic equations to determine both initial velocity and time of flight. Participants suggest checking the solution by substituting values back into the equations to confirm consistency with the problem's parameters. Accurate calculations are essential for solving projectile motion problems effectively.
TruthSeaker15
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A ball is thrown at an unknown speed at an angle of 30 degrees.

The initial and final height from the ground is 0 meters.

What speed should the ball be launched at in order for it to land on the ground 3 meters from the launch point?


Here is what I tried:

http://farm6.staticflickr.com/5548/10665499106_3549cac0cc_o.jpg

I got 5.829 m/s but I feel this is wrong.
 
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"I feel this is wrong" is OK, but then you should do something about your feeling. Why does that feel wrong? Can you check your solution somehow? In the end, we are not magicians here, you can do whatever we can.
 
It feels wrong because I'm not sure if my strategy was legitimate. I tried to check it, but I didn't really know how to.
 
You have used the kinematic equations to find the initial velocity. Now that you have the initial velocity, you can also find the time; then substitute the time and the initial velocity back into the equations and see whether you get what you should.
 

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