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Merry-go-round => what is conserved?

  • #1
A boy of mass m = 40 kg running with speed v = 4 m/s jumps onto the outer edge of a merry-go-round of mass M = 160 kg and radius R = 1.8 m, as shown in the picture above. The merry-go-round is initially at rest, and can rotate about a frictionless pivot at its center. You may assume that the inital velocity of the boy is tangent to the edge of the merry-go round.

Which of the following quantities are conserved throughout this problem for the system consisting of the boy and the merry-go-round?

A) only kinetic energy
B) kinetic energy and angular momentum
C) only linear momentum
D) linear momentum and angular momentum
E) only angular momentum

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I believe the answer is D, linear momentum AND angular momentum because both are conserved regardless of an inelastic or elastic collision right?

::
Can somebody please check out my answer and help me if it is wrong? Thank you very much in advance.
 

Answers and Replies

  • #2
Wait, wouldn't only the angular momentum be conserved since the boy's velocity changes after contact with the merry-go-round?

So only the angular momentum is conserved?
 
  • #3
LowlyPion
Homework Helper
3,090
4
It's an inelastic collision, so there's goes thinking kinetic energy would be conserved.

For linear momentum, when the boy contacts the rim of the go-round there is a force coming from the hub that resists the linear motion, but not the angular momentum. I think your choice of angular momentum only would be the correct answer.
 

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