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,, 68%[ 2053: Physics The Expert TA | Human-Ske x https:/luse11fl.theexpertta.com/Common/TakeTutorialAssignment.aspx HW 10 Begin Date: 10/16/2017 11:00.00 AM- Due Date: 10030/2017 11:00:00 AM End Date: 10/30/2017 11.00:00 AM (10%) Problem 9: An ice skater is spinning with her arms out and is not being acted upon by an cutemal toryue. 25% Part (a) when she pulls her arms in close to her body what happens to her angular momentum? It remains unchanped It decreases It increases t cannot be determined Grade Summary Deducties 0% Potential 10 Attempts nomaining I give llintx: 1%dedaction per hint. Hittiemain-EL Feedback:1% deaton per feedback. - 25% Part a) when she pulls her arms in, what happens to her moment of inertia? 25% Part(c) what happens to her angular speed when she pulls her arms in? 25% Part (d) What happens to her rocational kinetic energy when she pulls her arms in?Explanation / Answer
We use eqn,
Angular momentum = Moment of inertia*angora speed
L=I*w -------------(1)
a)
By law of conservation of angular momentum, angular momentum always remains constant it means it never increases or decreases.
Ths the correct option is It remains unchanged.
b)
I= mr^2
Where m is mass of the ice scatter, r= length of her arm.
From above eqn,
I r^2
Thus as length of arm ® decreases, moment of inertia (I) decreases.
c)
When she pulls her arms in her moment of inertia(I) decreases. From eqn (1) we can sat that I is inversely proportional to angular speed w
Thus
I 1/w
As I decrease w increases.
Thus correct option is angular speed increases.
d)
KE=1/2Iw^2
When I decreases w increases by same rate. But KE is directly proportional to w^2
Thus when she pulls her arms in KE increases.
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