Work and Bernoulli Eqn in Rotating Frame with Constant Angular Speed

[notojosh]

Q 1:Consider a disk of radius R. This disk is rotating around its center with a constarnt angular speed of w. Find the necessary work to move a body of mass m radially with respect to the disk from r=a to r=b.

Q 2:The Bernoulli equation for a unit mass can be written as

gdz+1/2VdV+vdP=0

where g is the gravitational acceleration, z the height, V the speed of fluid, v the specific volume, and P the pressure.

Referring to the Problem 1, write the Bernoulli equaiton in a rotating frame with a constant angualr speed of w.

please help. I don't really get what the qeustion asks. What is the body of mass? I might get confused between it and a center of mass.
Thx.

 

[tiny-tim]

hi notojosh!

… Find the necessary work to move a body of mass m radially with respect to the disk from r=a to r=b.
…
What is the body of mass?

it just means "a body which has mass m"

(it's a special meaning of "of" …

we say "a person of average height", "a person of 50kg weight", "a maiden of fair countenance" etc )​

 

[notojosh]

I think something with mass m is on the disk and since the disk is rotating there is centrifugar force to move that thing from a to b...Does anyone have any idea how to calculate the work? Also how this is related in q.2?

josh

 

[tiny-tim]

hi josh!

work done is defined as force "dot" displacement

 

[Redbelly98]

I think something with mass m is on the disk

Yes, correct.

... and since the disk is rotating there is centrifugar force to move that thing from a to b...Does anyone have any idea how to calculate the work?

Check in your textbook or class notes for the definition of work. You will find an equation there you can use.