Wednesday

January 28, 2015

January 28, 2015

Posted by **Katie** on Friday, March 16, 2012 at 10:33pm.

What is the magnitude of the angular momentum of the system if it is rotating with an angular speed of 2.89 rad/s?

While the system is rotating, the children pull themselves toward the center of the board until they are half as far from the center as before. What is the resulting angular speed?

What is the change in kinetic energy of the system as a result of the children changing their positions?

- physics -
**Elena**, Saturday, March 17, 2012 at 12:25pmMoment of inertia of the board respectively the pivot point is

Io = m(L^2 + W^2)/12 = 9.4(4.5^2+0.3^2)/12 = 15.93 kg•m^2,

Moment of inertia of the system (board+2 point mass-ñhildren) respectively

the pivot point is

I = Io + 2mR^2 = 15.93 + 2•11•(4.5/2)^2 = 127.305 kg•m^2

An angular momentum

L = I•ω =127.305•2.89 = 367.9 kg•m^2/s.

In the second position: the separation of each point mass (child)

from the pivot point is r = L/4, then,

I1 = Io + 2mr^2 = 15.93+ 2•11•(4.5/4)^2 = 43.77 kg•m^2.

According to the law of conservation of

the angular momentum of the system

L = Iω = I1•ω1.

ω1= Iω/ I1 = 367.9/43.77=8.4 rad/s.

ΔKE = KE2- KE1 = I1(ω1)^2/2- I(ω)^2/2 =

= 43.77•(8.4)^2/2 - 127.305•(2.89)^2/2 =

= 1548-532=1016 J.

**Answer this Question**

**Related Questions**

physics - Two people (from the 1950s!) sit on opposite sides of a uniform board...

physics - Two people, one of mass 70 and the other of mass 65 , sit in a rowboat...

Physics - A playground merry-go-round made in the shape of a solid disk, has a ...

physics - Two people, one of mass 85 kg and the other of mass 50 kg, sit in a ...

math - the nufone communications company must run a telephone line between two ...

Physics - You stand at the end of a long board of length L. The board rests on a...

math - A. One board is one-third the length of another. Six times the sum of the...

physics - Persons A and B are standing on a board of uniform linear density that...

physics - two children sit at opposite ends of a 60 lb. 10 ft. seesaw which is ...

physics - A fulcrum is placed under the center of a uniform 4.00m long, 3.00kg ...