July 13th, 2012, 07:40 AM
Ok this one is really easy, probably anyone can do it.
John is on his bike travelling at 4 km/h towards west, and he felt an east wind; he peddled up to 7 km/h, and the wind according to him then turned to south-east wind.
What is the actual wind speed?
Last edited by Wise Man; July 13th, 2012 at 08:43 AM. Reason: mistake made
Indeterminate no values for the wind are known
Hehe my mistake. I forgot to mention... check first post again.Originally Posted by fiveworlds
The actual wind speed will be how fast the wind is moving.
This one has me stumped.
Its easy he hasnt given enough to actually calculate the wind speed hes just asking what actual wind speed is as in define it.
If he is heading due west and feels a wind from the east, i.e., a head wind, that means the wind is from the east, calm, or from the west but less than the cyclist's speed. If there is a north-south component of wind velocity, the cyclist would not feel a direct head wind. Therefore speeding up would only increase the felt velocity, not the direction, and he could not feel a southeast wind without changing direction. I claim that there is no solution to the problem.
Thats funny I made it a tail wind heading west along with cyclist???
Go on I'll say 5km/h.
Oops you're right. Still, he doesn't feel any north-south component, so it must be only an east wind. He can't change it to a southeast wind by pedaling faster.
Yes but he doesnt ask for the wind direction just speed. Speed being a scalar quantity has no direction and this is incalculable.
Are you saying you posted a problem which does not have a solution? Or what are you saying?
I did not post this wise man did. Speed is distance over time but neither quantites are given therefore the speed isnt calculable.
We have got information about how fast the cyclist is travelling and the change of wind direction with the increase in speed, we also have the new angle for the wind direction.
Correct but how fast was the wind travelling originally? it is unknown plus the cyclist should have little if any effect on the wind dirction unless this is using chaos theory which it isnt.
To feel the wind it has to be moving faster than his 4km/h starting speed as the wind is moving forward from behind the cyclist, but less than the 7km/h because of the change in direction.
If you think so but there is no evidence that the cyclist caused the change in wind direction it could have change solely due to time a factor which seems to be absent here the cyclist could have cycled for a week before he reached 7km.
But that is speculation, we have to go on the facts presented, that only leaves the acceleration from 4km/h to 7km/h as the only explantion for change in wind direction.
Is this not more a basic physics question? The information seems pretty ambiguous to me.
Fine 2.8284km/h southwest from cos45*4
Hang on my bad
5.6568km/h
Thats 4/cos45
fiveworlds, just a tip. If you ever make a mistake, you can edit your post by clicking on the "Edit" button on the bottom right corner of the particular post. That way you don't have to constantly post new or corrected information.
Also, is that your answer? (I assume that's degrees)
My problem with that though is that is velocity not speed hence i havent awnsered the question.
Alright enough. Chrisgorlitz answered correctly: 5 km/h.
fiveworlds you seem to be confused: the wind direction changed according to the cyclist, but the actual wind direction and speed never changed.
I should have clarified the question further, sorry guys, I never thought this would cause so much arguments.
Also, by speed, I mean pure speed, I did not ask for direction.
Cool.
That was km per hour southwest halo
People get confused by the term ' south-east wind '.
It actually is wind blowing to the north-west.
Last edited by Wise Man; July 13th, 2012 at 01:00 PM.
Hey there's always arguments, means you've made a good puzzle.
Just explain it's all to do with triangles.
I know. I'm talking about the cosine part.
Just to help clarify the situation, what was the direction?
The triangles are easy though that wind blowing north west i never would of thought of. i still think you confused velocity and speed though.
Still confused. This is a trigonometry problem. No?
Yeah just use a triangle 4 on top and an angle of 45 and 90 from there get the hyp this will get the required velocity
Cosx equals adjacent/hypoteneuse
I have a diagram, but I don't have my scanner with me. And I don't have a good program to draw it with, so I believe I'm not of any use.
I have all those laws in my tables book do you not have one?
They are called the trigonometric identities Trigonometry Laws and Identities Math Sheet
My problem is just with visualizing this. I'm guessing a right triangle is involved by looking at your approach, but I fail to see how its ratios and the speed of the wind relate.
If the wind is blowing to the northwest, how is it directly at the back of a cyclist who is going west?
Yeah its a right triangle halo its a method used in physics to find the resultant of two vectors.
My big mistake. The cyclist should be going south.If the wind is blowing to the northwest, how is it directly at the back of a cyclist who is going west?
I really hate myself, I've created a chaos puzzle.
QUOTE=Wise Man;337154]Ok this one is really easy, probably anyone can do it.
John is on his bike travelling at 4 km/h towards west, and he felt an east wind; he peddled up to 7 km/h, and the wind according to him then turned to south-east wind.
What is the actual wind speed?[/QUOTE]
If John travels at 4mph towards th west and felt an east wind in his back, this means that he must have had a tailwind of greater than 4kmph. When John reaches 7kmp the wind shifts south-east, but John still feels a south-east tailwind thus the tail wind must have been greater than 7mph.
I didn't take the time to calculate angular windspeed loss of a south-east wind traveling westward on an object traveling west. However the westward motion of the south east wind must still be exceeding his 7mph. Say @ 50% loss of westward motion the wind speed should be around 12 mph is my guess.
Last edited by Write4U; July 14th, 2012 at 07:19 PM.
I claim the speed to be x+7.25042296/2root x^2 + 7.25042296x + 16
My big mistake. The cyclist should be going south.If the wind is blowing to the northwest, how is it directly at the back of a cyclist who is going west?
I really hate myself, I've created a chaos puzzle.
Hey my friend no probs, you created a fun puzzle, we managed to decipher it and even solve it, and we all learned the correct process for solving such puzzles so well done.
Ill have to agree with chris there
Thanks guys for the complemnts, next time I'll be sure to make things right!
Now that the game has been declared invalid, what was the answer?
That was the answer to puzzle as it was supposed to be. Think of a rectangle 4 high and you have the diagonal at 7 it's pretty easy to work out the lenght at 5. The 4, 5 and 7 form the triangle at what should be 90 degrees by 50 degrees by 40 degrees.
ok, 5 was my original answer until you introduced 7 mph (in a straight line).
Obviously you are into math and I should like to know if, using the instructions as given , my answer (which assumed a windshift to south east instead of a left turn by the biker.) came close.
Chris all your 5 does is show at what speed the cyclist would have felt a north or south wind
I think the awnser is just incalculable which was my first guess.
How do you come to feeling any wind at all, when traveling north @ 7mph, with a 5mph wind behind you. If anything the biker would still feel only an apparent headwind.That was the answer to puzzle as it was supposed to be. Think of a rectangle 4 high and you have the diagonal at 7 it's pretty easy to work out the lenght at 5. The 4, 5 and 7 form the triangle at what should be 90 degrees by 50 degrees by 40 degrees.
Actually the situation remains relative the same, you have just turned the travel system by 90 degrees. In effect the only thing that changes IS the wind direction, but to the biker it makes no real difference at all. He will feel a headwind in either direction.
Last edited by Write4U; July 14th, 2012 at 09:07 PM.
.
For those who are still confused, look at this!
http://www.thescienceforum.com/attac...-me-noname.jpg
Haha. All Wise Man needed was a single post and the crapstorm commenced!
I'm still confused though. It's a pretty good puzzle I have to say. How can I tell? Because it's puzzling as hell! I have no idea how to visualize this math/vector/trigonometry/physics problem even with the diagram.
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