- #1
member 428835
Homework Statement
The picture is too tough to draw online, so I've attached a picture of it. The illustrated mechanism shows two springs both with a known spring constant ##k## and rest length of ##2R##. One end of the top spring is fixed above a wheel and the other end is attached to the wheel that may rotate but not move. The other spring also has one end attached to the wheel, while the other end of this spring is at some user-selected distance ##(x,y)##.
I am trying to find the total energy given some location ##(x,y)##.
Homework Equations
Spring energy ##k(L-2R)^2/2## where ##L## is the length of the spring.
The Attempt at a Solution
Energy ##E## is $$E = k(L_1-2R)^2/2+k(L_2-2R)^2/2$$ So all I need to do to express energy as a function of ##x,y## is write ##L_1## and ##L_2## in terms of ##x,y##. To find ##L_1## let's use law of cosines:
$$L_1^2=(3R)^3+R^2-2\cdot3R\cdot R\cos\theta$$ I could find the length of ##L_2## the same way: instead of using ##\theta## I would use ##\pi-\theta##. One side of the triangle has ##L_2##, another has length ##R##, and the last has length ##\sqrt{x^2+y^2}##. But this is where I run into problems. Specifically, how to I express ##\theta## as a function of ##x,y##?
Mathematically, ##\theta## does not depend on ##x,y##. But physically it does, so there must be some physical law I'm not accounting for. Any ideas?
I should say, ##\theta## is the state variable and that ##x,y## are the independent parameters; does that imply it is independent on ##x,y## and I need not bother finding a relation?