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May 14th, 2015, 06:45 AM   #1
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Free Fall Motion.

A mine inspector has run into trouble 30m down an open vertical shaft. To summon help he fires a distress flare straight up the shaft. In order for the flare to be seen, it must reach at least 10m above the ground level. What is the least speed with which it must be fired?

I know that $\displaystyle s=30$ and $\displaystyle a=9.8$. I don't really understand the question. Can anyone explain the question?

P/s. Thanks for you guys, I can now solve those easy questions for 'SUVAT'. But when it comes to this kind of question, I don't really understand.
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May 14th, 2015, 07:18 AM   #2
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I think you're kind of looking at the problem and assigning numbers to letters rather than thinking about the situation as a whole.

Rather than just post the answer, I'll give you a couple of hints to think about.

1. If you haven't already done so, draw a diagram.

An aside on diagrams... just fyi

Seriously... drawing diagrams helps SO much! Whenever you have a tricky problem, the first thing you should do is make a simple sketch of the problem on paper. It doesn't have to be the Mona Lisa, it just helps you see what is happening and imagine the situation more easily. I've tutored students in the past who "magically" got better at mathematics or physics simply because I MADE them draw diagrams.

2. The question asks for a speed.
- If the initial firing speed of the flare is too low, what happens?
- If the initial firing speed of the flare is too high, what happens?
- which situation is okay to have and which one is not okay to have? and why?
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