A solid sphere rolls down without slipping. Fraction of KE that is rotational:
A5/7
B2/5
C1/2
D2/7
Answer & Solution
Correct answer: D. 2/7
KE_rot/KE_total = (1/2) I omega² / [(1/2)Mv² + (1/2)I omega²] = (I/MR²) / (1 + I/MR²) (using v = omega R). For sphere I/MR² = 2/5: ratio = (2/5)/(1 + 2/5) = (2/5)/(7/5) = 2/7. So 2/7 of KE is rotational.
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