A kid runs towards the edge of a merry-go-round that is not rotating and jumps o

Question

A kid runs towards the edge of a merry-go-round that is not rotating and jumps on. The merry-go-round then rotates with a constant angular velocity ?. Assume that the kid has a mass of 40 kg and is initially running at a speed of 4 m/s tangent to the edge of the merry-go-round. The merry-go-round is a uniform disk with a mass of 80 kg and a radius of 2 m. Assume that it rotates without friction.
What is the initial angular momentum Li of the system (kid plus merry-go-round)?
320.0 kg m2/s
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Your receipt no. is 158-9625 Previous Tries
What is the final angular momentum Lf of the system?
kg m2/s
Remember that angular momentum is conserved if there are no external torques.
Incorrect. Tries 1/2 Previous Tries
What is the final moment of inertia If of the system after the kid jumps on the merry-go-round?
kg m2
Remember that the final moment of inertia If = Idisk (merry-go-round) + Ikid, where the kid is a point mass at radius r.
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What is the final angular velocity ?f of the merry-go-round (with the kid riding)?
1.000 radians/s
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Your receipt no. is 158-2886 Previous Tries
What is the speed of the kid riding on the edge of the merry-go-round?
2.000 m/s
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Your receipt no. is 158-585

Explanation / Answer

angular momentum is conserved, so the final is same as initially

final angular momentum:
320.0 kg m2/s

Idisk= (1/2)80(2)2

Idisk=160

Ikid=(40)(2)2

Ikid=160

Itotal=Idisk+Ikid

Itotal=160+160

Itotal=320 kg-m2

Hope that helps

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