# Equilibrium of Particles

• hdp12
In summary, the problem involves finding the weight of block D using the equation F=-kx and the attached picture of the student's work. The student is stuck and unsure how to proceed, but has been given a tip to consider the ratio between "Facx" and "Facy" and to keep in mind the unstretched length of the spring AB is 3 meters, not 2 meters. They have also been reminded to use trigonometric ratios to find the weight of block D accurately.

## Homework Statement

Here is the problem that I am stuck on in my mechanics class.

F=-kx

## The Attempt at a Solution

See the attached picture of my work
I'm so stuck. I don't know what to do from here.

Why do you think the change in length of spring AB is 3 meters?

P.S.
Just a tip, there's no reason to find the angles spring AB makes; you only care about the sine or cosine of the angles which corresponds to ratios of the sides of the triangle. Finding (and rounding) the angle, like you did, may lead to less accuracy in the final answer.

What can you say about the ratio between "Facx" and "Facy"?

Nathanael said:
Why do you think the change in length of spring AB is 3 meters?
Because the unstretched length has been taken as 2m instead of 3m.

Nathanael said:
What can you say about the ratio between "Facx" and "Facy"
tan(45)=FACy/FACx or, they're directly proportional bc tan(45) = 1
FACy = FACx
What do I do with this?

hdp12 said:
tan(45)=FACy/FACx or, they're directly proportional bc tan(45) = 1
FACy = FACx
What do I do with this?
You calculated FACx so now you know FACy. You also calculated FABy. So what is the weight of block D?

But actually you calculated incorrectly, you'll need to recalculate (but I think you had the right idea). The problem says the unstretched length is 3 meters, not 2 meters.