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Any math people in here?

A photo of rightsaidfred rightsaidfred
Not sure where to post math questions, but this seems like the most fitting spot in the forum. It's not homework. I mostly study this stuff independently now. Here's what I think is a pretty tough question.

A railroad bridge is 20 m above, and at right angles to, a river. A person in a train travelling at 60 km/h passes over the center of the bridge at the same instant that a person in a motorboat traveling at 20 km/h passes under the centre of the bridge. How fast are the two separating 10 seconds later?


Any ideas? I do have the answer.
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6 replies
 
A photo of iliketurtles iliketurtles
What's the answer? I got 17.46 m/s (I did round a lot cause I got lazy) by expressing the distance between them as a function (Pythagorean theorem). Also I converted everything into m/s because the answer asks for seconds...and km/h is just stupid :)
After I made the function I just derived it (chain rule) then plugged in 10 into whatever variable you assigned to time.
Hopefully I'm not wrong or else I'd just be really, really, really, really embarrassed.
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A photo of rightsaidfred rightsaidfred
The question does actually ask for the answer in km/h. But yeah that's the answer I got. Sweet!
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A photo of iliketurtles iliketurtles
Ahh, I hate working in km/h though :( oh well haha
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A photo of EricF14 EricF14
To go from km/h to m/s and vice versa, just work out the units.

Ex: To find what 1 m/s is in km/h...

( 1 m/s ) * (1 km / 1000 m) * (60 s / min) * (60 min / hr) = 3.6 km/h

Cancel units and you should get that answer
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A photo of rightsaidfred rightsaidfred

@EricF14 wrote
To go from km/h to m/s and vice versa, just work out the units.

Ex: To find what 1 m/s is in km/h...

( 1 m/s ) * (1 km / 1000 m) * (60 s / min) * (60 min / hr) = 3.6 km/h

Cancel units and you should get that answer



I'm sure he knows how to do it. He was just saying how terrible km/h are to work with. m/s is always better.
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A photo of iliketurtles iliketurtles
I know how to do it, just think it's annoying... :P
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