gc textbook chapter 8 Rotational Motion (id: 023a5d902)

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本题目来源于试卷: gc textbook chapter 8 Rotational Motion，类别为 unclassified

[问答题]
Why is it more difficult to do a sit-up with your handst68otaebd 67 xmtvl:j.k m0h 6 behind your headw ;9+;- u.ihg7s*qude 2b1mxgk p cowznzk-c( than when your arms are stretched out inun;- p1o (b9cz ks h2z;*x.kwcd7umgq+ egi-w front of you? A diagram may help you to answer this.

参考答案:

When you do a sit-up, torque from your abdomen muscles must rotate the upper half of the body from a laying-down position to a sitting-up position.  The larger the moment of inertia of the upper half of the body, the more torque is needed, and thus the harder the sit-up is to do.  With the hands behind the head, the moment of inertia of the upper half of the body is larger than with the hands outstretched in front.

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