Writing equations in cylindrical coordinates (need work checked again please)

[clickcaptain]

Could someone tell me what I'm doing wrong? thanks!

Homework Statement

Write the equation is cylindrical coordinates

7x² + 7y² = 2y

r = ? (has to be in the r = ? format)

Homework Equations

r² = x² +y²
x = rcos(θ)
y = rsin(θ)

The Attempt at a Solution

7x² + 7y² = 2y

7(x² + y²) = 2y

7(r² = 2rsin(θ)

r² = (2rsin(θ))/7

r = sqrt((2rsin(θ))/7)

 

[HallsofIvy]

I think it would be better to leave it as $r^2= (2/7) sin(\theta)$ rather than taking the square root, but, yes, that is correct.

 

[clickcaptain]

its an online submission that has r = "enter here" , but i keep getting that its a wrong answer, is there any other way that this could be written?

 

[Defennder]

Note that you forgot to cancel out r on both sides of the equation. Don't express r in terms of r in the final answer.

 

[crisy]

Anybody have any idea about tramsforming the momentum equation into 2-D cylindrical co-ordinates...i've already derived the momentum equation from first principle but have difficulty with the transformation to cylindrical co-ordinates

 

[Defennder]

Hi, if you have a separate question you should post it in a new thread so that others can aid you. Sometimes people don't bother reading through a thread which already has several replies.