Dependent motion problem with ropes

[theBEAST]

Homework Statement

I attached the problem with my attempt.

The problem I have is that I have two unknowns. I think my set up is wrong. Does anyone know where to put the datum/set up this question?

Thanks!

 

[gneill]

Homework Statement

I attached the problem with my attempt.

The problem I have is that I have two unknowns. I think my set up is wrong. Does anyone know where to put the datum/set up this question?

Thanks!

What are your two unknowns? Remember, you're looking for dependencies between certain length changes.

 

[theBEAST]

What are your two unknowns? Remember, you're looking for dependencies between certain length changes.

I know it's A and C but I don't know how to get rid of B :S

 

[gneill]

I know it's A and C but I don't know how to get rid of B :S

Here's your drawing with the distances labeled.

Your equation is:

L = SA - SB + 2SC

What you're looking for is the rate of change of SA with respect to a rate of change of SC. So rearrange your formula to have SA on the left and the rest on the right. Now, are you familiar with calculus (derivatives)?

 

[theBEAST]

Here's your drawing with the distances labeled.

Your equation is:

L = SA - SB + 2SC

What you're looking for is the rate of change of SA with respect to a rate of change of SC. So rearrange your formula to have SA on the left and the rest on the right. Now, are you familiar with calculus (derivatives)?

Oh... I see, so if you take the derivative Sb and L are eliminated since they are constant?

 

[gneill]

Oh... I see, so if you take the derivative Sb and L are eliminated since they are constant?

Yup.