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Old Oct 24th 2010, 06:13 PM   #1
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Horizontal/Vertical Speed Question

"A fireman is standing at the edge of the roof of a 50 m tall building. He is directing a stream of water from his hose towards another building across the street that is on fire. The water is launched so that it has inital horizontal speed of 10 m/s and vertical speed of 20 m/s and takes 2 seconds to reach the burning buildin. The street's width must have been _____ while the water will strike the building at a heigh (from the ground) of ______."

I can't find what formulas to use for vertical/horizontal speeds. Help would be greatly appreciated. Thank you.
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Old Oct 24th 2010, 09:29 PM   #2
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The speed of the water along the horizontal would be given by:

Speed = Distance / Time

As the horizontal speed is 10 m and the time 2 seconds, what is the horizontal distance, which is the street's width?

Along the vertical, you have another equation. The one I tld you earlier.

s = ut + 0.5 at^2

The initial speed here is 20 m/s, your time 2 s and the acceleration due to gravity is a.

Depending on the directions that you take, you will have to take the acceleration as negative or positive, but my advice is to take the upwards direction as positive.

Hence, your vertical initial speed is + 20m/s, the acceleration due to gravity is then - 9.8 m/s^2 (or you can use 10 m/s^2 depending on what value you are asked to use).

Post what you get!
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