An object is in uniform circular horizontal motion at the end of a chord of length L. Its tangential speed is v. The chord is pulled in to length 0.5L in such a way that the tension in the chord remains constant. As a result, the tangential speed:
a) remains constant
b) increases to 2v
c) decreases to 0.5v
d) increases to 1.4v
e) decreases to 0.7v
The correct answer is E.
This can be solved using T = m * v^2/r approach. I get this, and I know how this works.
The Attempt at a Solution
Here's what I though initially: we do not have any net torques on the system [using an analogy of planetary motion around the sun, where angular momentum is conserved, substituting Tension force for gravitational force], so angular momentum has to be conserved.
Li = Lf
[m*v*r]i = [m*v*r]f
I eliminate the m's, and then plug:
v*L = x * 0.5 L
thus x = 2v, which is b, an incorrect answer.
Could anyone please explain why this approach is incorrect?
Thanks in advance for the assistance!