- #1
Rubber Ducky
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Homework Statement
A rod of length [itex]L_0[/itex] moves with a speed [itex]v[/itex] along the horizontal direction. The rod makes an angle of [itex]θ_0[/itex] with respect to the x'-axis.
(a) Show that the length of the rod as measured by a stationary observer is given by
[tex]L=L_0\sqrt{1-\frac{v^2}{c^2}cos^2θ_0}[/tex]
(b) Show that the angle that the rod makes with the x-axis is given by the expression
[tex]tanθ=γtanθ_0[/tex]
(Take the lower end of the rod to be at the origin of the primed coordinate system.)
Homework Equations
[tex]γ=\frac{1}{\sqrt{1-\frac{v^2}{c^2}}}[/tex]
[tex]L=\frac{L_0}{γ}[/tex]
[itex]{L_0}^2=(x')^2+(y')^2[/itex] and [itex]L^2=x^2+y^2[/itex]
The Attempt at a Solution
Let x and y be the rod's length and height (picture the rod forming the hypotenuse of a right triangle):
[itex]x'=L_0cosθ_0[/itex]
There is no movement in the y (or y') direction, so [itex]y'=y=L_0sinθ_0[/itex]
Meanwhile, the x component will contract in the non-prime reference frame, so [itex]x=\frac{x'}{γ}=\frac{L_0cosθ_0}{γ}[/itex]
Thus [itex]L^2=x^2+y^2=\frac{L_0^2cos^2θ_0}{γ^2}+L_0^2sin^2θ_0[/itex]
The algebra gets messy at this point, and I'm not sure what methods I should be using to yield the required form. I looked at my trig identities but none really seemed to fit the situation. And hopefully I haven't made a silly error in the physics side of things!