1) Two men are carrying a uniform plank of mass 5.6 kg and length 2.3 meters. A box of mass 108.4 kg is placed a distance 0.9 meters from the first man. Find the force applied by the second man.(adsbygoogle = window.adsbygoogle || []).push({});

Here what I did:

first man = force 1, second man force 2

F1 + F2 - mg = 0

F1 = (1.4)(5.6)(9.81) = 76.9104

F2 = mg - F1 = ((108.4)(9.81)) - 76.9104 = 986.4936

But the correct answer is 443.58. What did I do wrong?

2) A hollow ball of mass 1.9 kg and radius 0.1 meters begins rolling a distance 1.1 meters down a plane inclined at an angle 26 to the horizontal. Find its speed at the end.

Here is what I did:

Potential energy = (1.9)(1.1sin26)(9.81) = 8.988

KE = (1/2) (I) (w)^2

I=(2/3)(1.9)(0.1)^2 = 0.0127

PE = KE so, 8.988 = 0.00635w^2 ----> w = 37.622

w=v/r ----> v = (37.622)(0.1) ----> v = 3.76

But the correct answer is 2.38. What did I do wrong? Please help. Thanks.

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# Homework Help: HELP: Force and Inertia

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