Hi there!
We can use the conservation of angular momentum to solve.
Recall the equation for angular momentum:
We can begin by writing out the scenario as a conservation of angular momentum:
= moment of inertia of the merry-go-round (kgm²)
= angular velocity of merry go round (rad/sec)
= final angular velocity of COMBINED objects (rad/sec)
= moment of inertia of boy (kgm²)
= angular velocity of the boy (rad/sec)
The only value not explicitly given is the moment of inertia of the boy.
Since he stands along the edge of the merry go round:
We are given that he jumps on the merry-go-round at a speed of 5 m/s. Use the following relation:
Plug in the given values:
Now, we must solve for the boy's moment of inertia:
Use the above equation for conservation of momentum: