Angular momentum and change in velocity

[physgrl]

Homework Statement

A turntable has a moment of inertia of 2.5 x 10-2 kg m2 and spins freely at 33.3 rev/min. A 0.25 kg ball of putty is dropped vertically on the turntable at a point 0.20 m from the center. What is the new angular speed of the system?

a. 41 rev/min
b. 24 rev/min
c. 33 rev/min
d. 27 rev/min

Homework Equations

L=Iω
p=mv
L=r*p

The Attempt at a Solution

i tried to do Iω=(I+mr)ω(final)
i got 27 rev/min
the real answer is supposed to be 24rev/min according to the answer key

 

[hage567]

Homework Statement

A turntable has a moment of inertia of 2.5 x 10-2 kg m2 and spins freely at 33.3 rev/min. A 0.25 kg ball of putty is dropped vertically on the turntable at a point 0.20 m from the center. What is the new angular speed of the system?

a. 41 rev/min
b. 24 rev/min
c. 33 rev/min
d. 27 rev/min

Homework Equations

L=Iω
p=mv
L=r*p

The Attempt at a Solution

i tried to do Iω=(I+mr)ω(final)
i got 27 rev/min
the real answer is supposed to be 24rev/min according to the answer key

Can you show the details of your calculation? We can't tell you what you did wrong if you don't show us your work!

 

[LawrenceC]

"i tried to do Iω=(I+mr)ω(final)"

Careful, mr does not have same units as I.

 

[physgrl]

Yeah that was my error thanks!