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Conservation of Angular Momentum and Kinetic Energy

Imagine a rod 2 meters long fixed at its center, 2 identical masses are placed 0.5 meters away on opposite sides , as the rod spins they slide towards the edges , according to the formula k.E.=0.5*I*ω2 the kinetic energy decreases , but since its a closed system why does the kinetic energy decrease ?

 

Answer:

The decrease in KE accounted by the work done in displacing the masses

What is the mechanical energy of a bird on top of a moving Ship?

A bird is at rest on d top of a stick of moving ship….!! what is the mechanical energy that exists in the bird ???” – This question was posted by Fatima

Answer: The mechanical energy of the bird is both Potential and Kinetic as the bird is at a height with respect to ground and the bird is in motion along with the ship.

(Any deeper discussion is welcome)

A question from Kinetic energy

Atul asked:

A lorry and a car moving with the same KE are brought to rest having same retarding force .which one of them should come at rest at shorter distance.

 

Ans:

According to Work Kinetic Energy theorem

Both should stop travelling the same distance

(This was a quick answer without a deep thought. If the readers have a diffrent opinion, please comment)

A question from photoelectric effect

Jyothir Asked:

In photoelectric effect, what happens to the photon after it collides elastically with the electron ?

 

Ans:

The photon is completely absorbed by one electron, the energy of the electron provides the work function which is equal to the binding energy of the electron and the balance energy appears as the electrons Kinetic energy.

As Einstein’s Photo electric equation suggests

KE = h (v-vo)

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