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# Some help with this Projectile Motion question please? watch

1. I need to know how you would find the velocity at which the particle leaves the elevated platform on this diagram for a computing program I'm coding. The particle leaves a 150m high platform at 30 degrees and travels 30,000m.

I think it will contain simultaneous equations some where but I'm truly stumped. I can do Projectile Motion problems with elevated platforms but I'm struggling to work backwards to find the velocity.

(I'm using 9.8 for g)

If you could explain how to find the answer that would be great, thanks.
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2. (Original post by JamieOH)
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Let be the initial velocity.

So vertically:

Horizontally:

Sub this into the vertical equation, the first term will cancel, and leave you with a from the term. As all values are known, you can just do some manipulation.

Spoiler:
Show

Let be the horizontal displacement, be the vertical displacement, be the initial launch velocity. Assume the projectile is launched at above the horizontal.

Horizontal:

Vertically:

Subbing in the expression for t:

Re-arranging:

3. (Original post by Phichi)
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Many thanks. I guess it was kinda simpler than I thought, I approached it the complete wrong way aha.
4. (Original post by JamieOH)
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Check my post again. It'll give you a basis for code, assuming you're using unknown parameters. The best way to do it would be to write a basic expression as above, then either make a prompt to enter the variables, or assign them in the code.

Remembering the signs on x and y ofcourse. As y in your case, using the above would be -150.
5. (Original post by Phichi)
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I don't understand why it wouldn't be like:

Is not not like this and then expanded? What am I seeing wrong?

Also thanks for the more in-depth explanation! Very helpful.
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6. (Original post by JamieOH)
..
It's not . It's .

For example:

7. (Original post by Phichi)
It's not . It's .

For example:

Oh my god, my mind blanked. Thanks.
8. (Original post by JamieOH)
Oh my god, my mind blanked. Thanks.
No worries, you don't have to use a template. I just assumed if you're coding, you might want to use more than one set of values, or it wouldn't really be a program, more just one calculation.
9. (Original post by Phichi)
No worries, you don't have to use a template. I just assumed if you're coding, you might want to use more than one set of values, or it wouldn't really be a program, more just one calculation.
Yes it asks what values are available to the user and then works out what it needs to do to solve certain things. I'm calling it a suvat calculator, just a little project I decided to do to help me in both Computing and Physics. I've done all the basics and I got a little stuck on not knowing the angle/velocity but thanks to you I can get cracking! (:

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Updated: January 26, 2015
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