Length of Spring: How Can the Unstretched Length Be Determined?

[ttiger2k7]

[SOLVED] Length of Spring

Homework Statement

A load of weight 400 N is suspended from a spring and two cords that are attached to blocks of weights 3W and W as shown. Knowing that the constant of the spring is 800 N/m, determine (a) the value of W, (b) the unstretched length of the spring.

http://img406.imageshack.us/img406/472/13213uv7.jpg

Homework Equations

$$F_{s} = -k x$$

The Attempt at a Solution

I have already worked through part (a), getting 62.8 N for W and in the process I got 281.712 for the $$F_{s}$$ of the system above.

Now from the picture above, I can figure that the length AB is 1110 mm using Pythagoreans. Whether that is relevant or not to figuring (b) out, I am not sure. I'm thinking that I need to find what the $$F_{s}$$ would be if there were no forces acting on the spring.

 

[OmCheeto]

Homework Statement

A load of weight 400 N is suspended from a spring and two cords that are attached to blocks of weights 3W and W as shown. Knowing that the constant of the spring is 800 N/m, determine (a) the value of W, (b) the unstretched length of the spring.

http://img406.imageshack.us/img406/472/13213uv7.jpg

Homework Equations

$$F_{s} = -k x$$

The Attempt at a Solution

I have already worked through part (a), getting 62.8 N for W and in the process I got 281.712 for the $$F_{s}$$ of the system above.

Now from the picture above, I can figure that the length AB is 1110 mm using Pythagoreans. Whether that is relevant or not to figuring (b) out, I am not sure. I'm thinking that I need to find what the $$F_{s}$$ would be if there were no forces acting on the spring.

I would look at the relevant equation and attempt to determine if it can be expanded to include initial and final values.

 

[rosstheboss23]

You can determine angles using SOH CAH TOA. From there you can use components to work out your answer more precisely.

 

[ttiger2k7]

double post...

 

[ttiger2k7]

I would look at the relevant equation and attempt to determine if it can be expanded to include initial and final values.

Thanks, I got it!