A physics student is sitting on a frictionless platform that is rotating with an
ID: 2265430 • Letter: A
Question
A physics student is sitting on a frictionless platform that is rotating with an angular speed of wi=2.2rad/s. His arms are outstretched, and he is holding a heavy weight in each hand. The moment of inertia of the student, the extended weights, and the platform about the rotation axis is Ii=7.9kg*m^2. When the student pulls the weights inward toward his body, the moment of inertia decreases to If=5.3kg*m^2 and his angular speed increases to 3.28rad/s. By how much is the kinetic energy of the system increased?
A physics student is sitting on a frictionless platform that is rotating with an angular speed of wi=2.2rad/s. His arms are outstretched, and he is holding a heavy weight in each hand. The moment of inertia of the student, the extended weights, and the platform about the rotation axis is Ii=7.9kg*m^2. When the student pulls the weights inward toward his body, the moment of inertia decreases to If=5.3kg*m^2 and his angular speed increases to 3.28rad/s. By how much is the kinetic energy of the system increased?Explanation / Answer
I1= 7.9 kg*m^2
w1= 2.2 rad/s
I2 = 5.3 kg*m^2
w2= 3.28 rad/s
increase in K.E.= 1/2*(I2*w2^2 - I1*w1^2)
= (5.3*3.28*3.28 - 7.9*2.2*2.2)/2
=18.78/2
=9.39 J
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