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# Daily Archives: September 25, 2011

## 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 ?

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

## Why some substances are transparent while some others are opaque

Why some substance being solid enable light to pass through them (like glass, diamond (the hardest substance etc) but other who have less density do not permit refraction?

## Electromagnetic induction in outer space and energy conservation

“lets pretend we are in space. and there  I have a permanent magnet rotor that and around it are copper windings. They do not touch and everything is floating with minimum friction (because we are in space)
imagine a generator with no brushes or bearings….

now my question is :
if i spin the rotor, and electrons start flowing on the copper(electricity)
would there be a negative force on the rotor to make it stop faster ?

Thank you

(Posted by )

Waiting for public response

## If neutrino travels faster than light?

If neutrinos travel at the speed of light through a vacuum, and rarely interact with matter, how fast do they travel through the nucleus of an atom?

## Kinematics Numerical

1. A particle travels 20 m in 7th second and 24m in 9th sec. find initial velocity?
2. in a projectile motion , a body thrown from the ground ,at what angle both the vertical height and range will be equal?
3. The velocity v(cm/s) of a particle is given in terms of time t(in seconds) by the equation v = at+b/t+c. Dimension of a,b, and c are ?

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