A man stands on a freely rotating platform, as shown, holding an exercise dumbbell in each hand. With outstretched arms, his angular speed is 1.5 rad/s. After he has pulled his arms in, as shown, his angular speed is 5 rad/s. What is the ratio of his final rotational KE to his initial rotational KE? Explain any differences.

Question

A man stands on a freely rotating platform, as shown, holding an exercise dumbbell in each hand.  With outstretched arms, his angular speed is 1.5 rad/s.  After he has pulled his arms in, as shown, his angular speed is 5 rad/s.  What is the ratio of his final rotational KE to his initial rotational KE?  Explain any differences.

Help please. Use the correct equation then substitute the numbers into that equation

bobpursley · Answer

moving ars in decreases the moment of inertia, which if momentum is conserved, angular speed increases

momentums:
initialI*1.5=final*5
finalI/initialI=1.5/5

energy:
finalKE/initialKE= .5finalI*5^2/.5InitialI*1.5^2

or = 1.5/5 * (5^2/1.5^2)=5/1.5

Anonymous · Answer

What is the answer? Is it 1.998?