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## Homework Statement

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

## Homework Equations

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.

Thus:

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!