A merry-go-round (pictured) is sitting in a playground. It is free to rotate, but is currently stationary. You can model it as a uniform disk of mass 210 kg and radius 110 cm (consider the metal poles to have a negligible mass compared to the merry-go-round). The poles near the edge are 100 cm from the center.

Question

Someone hits one of the poles with a 9 kg sledgehammer moving at 17 m/s in a direction tangent to the edge of the merry-go-round. The hammer is not moving after it hits the merry-go-round.

How much energy |ΔE| is lost in this collision? (enter a positive number for the absolute value in Joules)

|ΔE|=

Answer 1

You forgot to mention that this problem is part if your 8.01 MIT exam and asking for help during your exam is a violation of the Honor Code.

Answer 2

And why exactly are you here?

Answer 3

you can work omega out of conservation of momentum.

then get rotational KE using that omega.

then the energy loss should be

initial KE_hammer - rotational KE

Answer 4

eh eh honor code eh eh eh

Answer 5

*you can work omega out of conservation of momentum*

do you add the momentum of inertia of the sledgehammer to the merrygoround?

cuz when I do, I get the wrong answer.

Answer 6

How would I get omega from here? Please help.

Answer 7

that one is obvious, no?

s = r * theta

ds/dt = r dtheta/dt

v = r * omega

Answer 8

I still don't get it..