Question

A gymnast dismounts the uneven parallel bars with some angular momentum about her transverse axis. Just after release, she is in a piked position. She then extends into a layout position before she lands. What happens as a result of this action?
a. Her moment of inertia increases and she rotates slower.
b. Her angular momentum decreases.
c. Her angular momentum increases.
d. Her moment of inertia decreases and she rotates faster.
e. none of the above

Answer 1

Answer:

a. Her moment of inertia increases and she rotates slower.

Explanation:

As we know that initially when she starts her motion she is in piked position due to which her whole mass is concentrated near the axis of rotation

So here the rotational Inertia of her body will be smaller

Now when is comes closer to the position of landing she extends into layout position due to which her mass will move away from the axis of rotation

Due to this the rotational inertia of her body will increase

now we know that there is no external torque on the system

so here angular momentum must be conserved

So we will have

$I\omega = constant$

so if rotational inertia is increasing then angular speed must be slower

so correct answer will be

a. Her moment of inertia increases and she rotates slower.