(c) Where did this increase in energy come from? (Select all that apply.) ( )kin
ID: 1786342 • Letter: #
Question
(c) Where did this increase in energy come from? (Select all that apply.)
( )kinetic energy of the platformair
( )resistance
( )your internal energy
( )mass of the weights
( )gravity
A force of magnitude F is applied horizontally in the -x direction to the rim of a disk of radius R as shown below. Write F and F in terms of the unit vectors î, J, and k, and compute the torque produced by this force about the origin at the center of the disk. (Use the following as necessary: F, R.) 2. -12 points Tipler6 10.P.049.soln My Notes Ask Your Teacher You stand on a frictional platform that is rotating at 1.6 rev/s. Your arms are outstretched, and you hold a heavy weight in each hand. The moment of inertia of you, the extended weights, and the platform is 9.5 kg m2. When you pull the weights in toward your body, the moment of inertia decreases to 5.3 kg m2. (a) What is the resulting angular speed of the platform? rev/sExplanation / Answer
1. F = - F i^
r = R j^
torque = r x F = R F (j x -i)
= R F k^
2. (A) applying angular momentum conservation,
Ii wi = If wf
9.5 x 1.6 = 5.3 wf
wf = 2.87 rev/s
(b) delta(KE) = (5.3) (2.87 x 2pi)^2 /2 - (9.5)(1.6 x 2pi)^2 /2
= 381.7 J
(C) Your internal energy
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