Question

A merry-go-round is a common piece of playground equipment. A 3.0-m-diameter merry-go-round with a mass of 250 kg is spinning at 20 rpm. John runs tangent to the merry-go-round at 5.0 m/s, in the same direction that it is turning, and jumps onto the outer edge. John's mass is 30 kg. What is the merry-go-round's angular velocity, in rpm, after John jumps on?

Answer 1

I've been using conservation of momentum:\[I_iomega_i+I_i \omega_i=I_f \omega_f+I_f \omega_f\]

I keep ending up with \[\omega=1.29 rad/s\] which amounts to 12 rpm. It's telling me I'm wrong.

Answer 2

I got 1.24rad/s or 11.84 rpm by keeping every number as it is and not rounding it off.
So I think you're absolutely right.

Answer 3

I have the same numbers and Mastering Physics is telling me it's wrong