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ma18
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Homework Statement
A particle moves with const speed v along the curve r(θ) = a(1+cos θ).
Starting with the general expression for the velocity vector v in polar coordinates solve for θ_dot in terms of v, k, and θ. What does the sign of θ_dot signify?
Homework Equations
v = r_dot*r_hat + r*θ_dot*θ_hat
v = v * v_hat
r(θ) = a(1+cos θ)
r_hat = x_hat cos Θ + y_hat sin θ
v
The Attempt at a Solution
r_dot = -a sin θ
solving for θ_dot:
θ_dot = (v - r_dot * r_hat)/(r*Θ_hat)
I am lost here, I think I am missing some important relation and something that comes out of the fact that the speed in constant but I don't know what.
Any help would be greatly appreciated thanks.Edit:
I think I've got it, since the magnitude of unit vectors are one and θ_dot is a scalar I can just stop at
θ_dot = (v - r_dot * r_hat)/(r*Θ_hat)
= (v*v_hat - r_dot * r_hat)/(r*Θ_hat)
= (v-r_dot)/r
= (v+a sin θ)/(a + a cos θ)
Is this right? What does the sign mean then, just the value?
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