A child is spinning on a bar stool waiting for his brother to get off work. He s
ID: 1296818 • Letter: A
Question
A child is spinning on a bar stool waiting for his brother to get off work. He spins with his arms out and his moment (kid and chair) of inertia is 3.24 kg m^2. His initiall angular velocity spinning in the chair is 5.87 rad/s. His brother is ready to leave and tosses the child a 2.27 kg bag of change. the child catches the bag of change while spinning and holds it at a distance of .20m from his axis of rotation. Treat the bag of change as a point particle.
A: What is the initial angular momentum of the system?
B: What is the final moment of Inertia of the system?
C: What is the final angular velocity of the system?
D: Find the initial and final kinetic energies of the system?
Explanation / Answer
A) L1 = I1*w1
= 3.24*5.87
= 19.02 kg.m^2/s
B) I2 = I1 + m*r^2
= 3.24 + 2.27*0.2^2
= 3.331 kg.m^2
C) L1 = L2
I1*w1 = I2*w2
w2 = I1*w1/I2
= 19.02/3.331
= 5.71 rad/s
D) Ki = 0.5*I1*w1^2
= 0.5*3.24*5.87^2
= 55.82 J
Kf = 0.5*I2*w2^2
= 0.5*3.331*5.71^2
= 54.3 J
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