During a jump to his partner, an aerialist is to make a quadruple somersault lasting a
time
. For the first and last quarter-revolution, he is in the extended orientation shown in the figure, with rotational inertia
around his center of mass (the dot). During the rest of the flight he is in a tight tuck, with rotational inertia
What must be his angular speed
in
around his centre of mass during the tuck?
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S i n c e t h e o n l y f o r c e a c t i n g o n h i m ( g r a v i t a i o n a l ) i s a c t i n g o n t h e C . O . M , a n g u l a r m o m e n t u m i s c o n s e r v e d 1 . I 1 ω 1 = I 2 ω 2 L e t t h e t i m e t a k e n t o p e r f o r m t h e f i r s t q u a t e r + l a s t q u a r t e r = t 1 N u m b e r o f r e v o l u t i o n s i n t 1 = 2 1 L e t t h e t i m e t a k e n t o p e r f o r m t h e r e s t o f t h e j u m p = t 2 N u m b e r o f r e v o l u t i o n s i n t 2 = 2 7 2 . 2 1 r e v = I 1 I 2 ω 2 × t 1 ( ω 1 = I 1 I 2 ω 2 f r o m a n g u l a r m o m e n t u m c o n s e r v a t i o n ) 3 . 2 7 r e v = ω 2 × t 2 D i v i d i n g t h e a b o v e t w o e q u a t i o n s , w e g e t 4 . t 2 − I 1 7 I 2 t 1 = 0 G i v e n : 5 . t 1 + t 2 = 1 . 8 7 S o l v i n g t h e a b o v e t w o l i n e a r e q u a t i o n s , w e g e t t 1 = 0 . 7 8 5 s t 2 = 1 . 0 8 5 s I n s e r t i n g t h e a b o v e v a l u e s i n e q 3 , w e g e t ω 2 = 3 . 2 3 r e v s − 1