Find the ration of the centripetal accelaration

[jandominic145]

The large blade of a helicopter is rotating in a horizontal circle. The length of the blade is 6.7m, measured from its tip to the center of the circle. find the ration of the centripetal accelaration at the end of the blade to that which exists at a point located 3.0m from the center of the circle?

the answer is 2.2

i don't know to get 2.2

 

[Cyosis]

Show us what you have attempted so far. Start with the formula for centripetal acceleration.

 

[jandominic145]

Show us what you have attempted so far. Start with the formula for centripetal acceleration.

centripetal acceleration
Ac = V^2/r

 

[Cyosis]

Yes and you know that the blade describes a circle. So how can you calculate v in terms of the radius and period?

 

[jandominic145]

Yes and you know that the blade describes a circle. So how can you calculate v in terms of the radius and period?

Ac = 6.7m^2/3m
= 44.89m/3m
= 14.96

the answer is 2.2 not 14.96

 

[Cyosis]

The length of the blade is 6.7m, how can that be equal to its speed? Length and speed are not the same! I will ask again how can you express v in terms of the radius and period?

 

[jandominic145]

The length of the blade is 6.7m, how can that be equal to its speed? Length and speed are not the same! I will ask again how can you express v in terms of the radius and period?

i didn't understand it

 

[Cyosis]

What part do you not understand and why are you ignoring my question for the second time? If you are unwilling to cooperate we're not going to get anywhere. I will guide you to the answer, but only if you cooperate.

 

[jandominic145]

What part do you not understand and why are you ignoring my question for the second time? If you are unwilling to cooperate we're not going to get anywhere. I will guide you to the answer, but only if you cooperate.

60 degrees

 

[Cyosis]

'the circle of degrees is 60' makes no sense to me. It is also irrelevant to the problem. For the third time now I will ask you the following question:

How can you express the speed v, in terms of the radius r, and the time it takes for one revolution T?

 

[jandominic145]

'the circle of degrees is 60' makes no sense to me. It is also irrelevant to the problem. For the third time now I will ask you the following question:

How can you express the speed v, in terms of the radius r, and the time it takes for one revolution T?

what is T revolution

 

[Cyosis]

As I said, the time it takes for one revolution, the period.

 

[jandominic145]

As I said, the time it takes for one revolution, the period.

how?

 

[Cyosis]

Could you be a little bit more specific when it comes to asking questions and giving answers. Single phrase 'sentences' really don't work well to convey a message. I do not see how the sentence you quoted from me can generate the question 'how'? How what?

 

[jandominic145]

Could you be a little bit more specific when it comes to asking questions and giving answers. Single phrase 'sentences' really don't work well to convey a message. I do not see how the sentence you quoted from me can generate the question 'how'? How what?

the time it takes for one revolution, the period.

 

[Cyosis]

We are having serious communication issues here. Do you know what a revolution is, do you know what a period is? If you do, explain both concepts to me.

 

[jandominic145]

We are having serious communication issues here. Do you know what a revolution is, do you know what a period is? If you do, explain both concepts to me.

i don't know what is revolution and period

 

[Cyosis]

The blade describes a circle, it rotates. After some time T the blade returns to its original position at that point in time it has done one full rotation called a revolution. The time it takes for the blade to make one circle is called the period. You want to know the speed of the blade at a distance r from the center.

 

[jandominic145]

The blade describes a circle, it rotates. After some time T the blade returns to its original position at that point in time it has done one full rotation called a revolution. The time it takes for the blade to make one circle is called the period. You want to know the speed of the blade at a distance r from the center.

R is 3 m

 

[Cyosis]

R can be all values in between 6.7 and 0. You have a formula for the centripetal acceleration with two variables r and v. r is known but v is not therefore we want to find v. I have been telling you to do this for the fourth time now.

If you pick a certain point on the propeller blade and let the blade rotate until it comes back to its original position. How much distance has that point traveled? hint: the blade describes a circle

 

[jandominic145]

R can be all values in between 6.7 and 0. You have a formula for the centripetal acceleration with two variables r and v. r is known but v is not therefore we want to find v. I have been telling you to do this for the fourth time now.

If you pick a certain point on the propeller blade and let the blade rotate until it comes back to its original position. How much distance has that point traveled? hint: the blade describes a circle

6.7m

 

[Cyosis]

Great another one phrase answer without any explanation to why you think that is the answer. Are you just guessing or what? The blade is 6.7m LONG and is rotating. I placed a point a distance r from the enter on the blade, never did I say the point was on the tip of the blade.

The blade is rotating it describes a circle do you see this? (answer this question)
Therefore the point on the blade follows the circumference of that circle. How much distance does the point move during one revolution? (answer this question)

 

[jandominic145]

Great another one phrase answer without any explanation to why you think that is the answer. Are you just guessing or what? The blade is 6.7m LONG and is rotating. I placed a point a distance r from the enter on the blade, never did I say the point was on the tip of the blade.

The blade is rotating it describes a circle do you see this? (answer this question)
Therefore the point on the blade follows the circumference of that circle. How much distance does the point move during one revolution? (answer this question)

i dunno

 

[Cyosis]

So you don't know a single one of those questions? I must say you don't make me feel like you are actually trying to understand this. So I am going to try one more time.

Do you understand and see how the blade describes the circumference of a circle when it starts rotating?
What is the circumference of that circle?

Answer both questions separately.

 

[jandominic145]

So you don't know a single of those questions? I must say you don't make me feel like you are actually trying to understand this. So I am going to try one more time.

Do you understand and see how the blade describes the circumference of a circle when it starts rotating?

the length is 6.7 m and the center of the circle is 3

 

[jandominic145]

i need to solve now

 

[Cyosis]

No that's wrong, besides that's not even what I asked. The center of the circle is at a distance 0, the 3m value is almost half way on the blade and the 6.7m value is at the tip of the blade. Read post #24 again and answer my questions.

 

[jandominic145]

No that's wrong, besides that's not even what I asked. The center of the circle is at a distance 0, the 3m value is almost half way on the blade and the 6.7m value is at the tip of the blade. Read post #24 again and answer my questions.

i did not understand how the blade describes the circumference of a circle when it starts rotating?
What is the circumference of that circle?

3.1416 is pi r

c=2(3.1416)r

 

[Cyosis]

That makes no sense. What you wrote there is $3.1416=\pi r$. Presumably this is the answer to the question what the circumference of the circle is? Well obviously this answer is wrong. Try again, what is the formula of the circumference of any circle?

 

[jandominic145]

That makes no sense. What you wrote there is $3.1416=\pi r$. Presumably this is the answer to the question what the circumference of the circle is? Well obviously this answer is wrong. Try again, what is the formula of the circumference of any circle?

c = 2 pi r

 

[Cyosis]

Yes so the distance the point on the blade travels is?

 

[jandominic145]

yes so the distance the point on the blade travels is?

18.8496

 

[Cyosis]

What did I say about randomly writing down a number or not. The point is at a distance r, I don't see how we can get a numerical value. So if the point is at a distance r from the center the circumference of the circle it describe is? Don't just show your answer also show your calculation.

Now remember that one revolution takes time T to complete. You now know the distance the point traveled and how long it took. So the speed of the point around the circle is?

Does a point on the tip of the propeller has the same period as a point on the center of the blade?

 

[jandominic145]

what did i say about randomly writing down a number or not. The point is at a distance r, i don't see how we can get a numerical value. So if the point is at a distance r from the center the circumference of the circle it describe is? Don't just show your answer also show your calculation.

Now remember that one revolution takes time t to complete. You now know the distance the point traveled and how long it took. So the speed of the point around the circle is?

Does a point on the tip of the propeller has the same period as a point on the center of the blade?

c = 2 (3.1416)(3)
c = 18.85

 

[Hootenanny]

jandominic145 - I suggest that you start being more helpful to those who are trying to assist you in your studies. Most people here are extremely patient and happy to help those people who are willing to put some effort into their studies. However, you must realize that everyone's time is finite and unless you start making more of an effort and actually try to solve the problems yourself without having the solution handed to you on a platter then you will quickly find yourself without any help at all.

Now, Cyosis has been more than helpful and has virtually given you the algorithm required to solve the problem several times. I suggest that you take a breath and then look at Cyosis' posts and see if you can solve the problem without asking any additional questions.