A bullet through a pendulum.

[gneill]

And what are some other possibilities of finding the initial velocity of the pendulum. why didnt 300(0.01) = (2.21)V' work? Because for a brief instant that the bullet does hit the block or the slight second its leaving the bullet is in the block, and momentum should be transferred no ?

The bullet and block are never one object moving with the same velocity. Simply occupying the same space does not count

 

[zaddyzad]

I don't fully understand why EK(bullet) = EK(bullet) + EP(bullet) doesn't work. The kinetic energy before and after the collision is constant, and so it the EP that the pendulum has. Why isn't the energy of the system being conserved.

 

[issacnewton]

whats the answer you got finally ?

 

[gneill]

I don't fully understand why EK(bullet) = EK(bullet) + EP(bullet) doesn't work. The kinetic energy before and after the collision is constant, and so it the EP that the pendulum has. Why isn't the energy of the system being conserved.

Energy is only conserved for perfectly elastic collisions. Otherwise, energy is always lost in the collision to various "loss" pathways such as frictional heating, sound, plastic deformation of materials, breaking of atomic bonds(tearing, breaking), and so on.

 

[zaddyzad]

Energy is only conserved for perfectly inelastic collisions. .

Though kinetic energy is only conserved in perfect elastic collision?

 

[gneill]

Though kinetic energy is only conserved in perfect elastic collision?

D'oh! My bad. Of course it's ELASTIC collisions only. I fixed the text in the original.