How Does a Wax Blob Affect the Angular Velocity of a Rotating Rod?

[nil1996]

Homework Statement

A rod of length L and mass M is pivoted at the center C such that it can freely rotate in vertical plane.Initially the rod is at horizontal position.A blob of wax of mass M falls vertically with speed V and sticks to the rod midway between center and one end.If the rod rotates with angular speed ω what will be the angular velocity in terms of V and L?

Homework Equations

none

The Attempt at a Solution

Can i use energy conservation here.The kinetic energy carried by the wax blob will be transferred into rotational energy.Is this approach right?

 

[ehild]

Homework Statement

A rod of length L and mass M is pivoted at the center C such that it can freely rotate in vertical plane.Initially the rod is at horizontal position.A blob of wax of mass M falls vertically with speed V and sticks to the rod midway between center and one end.If the rod rotates with angular speed ω what will be the angular velocity in terms of V and L?

Homework Equations

none

The Attempt at a Solution

Can i use energy conservation here.The kinetic energy carried by the wax blob will be transferred into rotational energy.Is this approach right?

No, the blob sticks to the rod, it is inelastic collision.

ehild

 

[nil1996]

So how do we calculate how much energy was useful from that collision?

 

[maajdl]

The description suggests a "Perfectly inelastic collision".
Read this:

http://en.wikipedia.org/wiki/Inelastic_collision#Perfectly_inelastic_collision

The system described there, a collision between two masses that stick together, is rather similar to the rod and mass system of your exercise. The energy is not conserved.
In your exercice, is there a conserved quantity?

 

[nil1996]

i think using conservation of angular momentum will get me the answer.right?

 

[maajdl]

Yes, but you should justify this assumption.