- #1

PhysicsDaoist

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(Cut from the lecture)

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*Kinetic energy is conserved.*

All the kinetic energy is in the tennis ball; nothing is in the wall.

The wall has an infinitely large mass, but the momentum of this tennis ball has changed by an amount 2 mv.

So now here you see in front of your eyes a case that the wall has momentum, but it has no kinetic energy.

That the wall has momentum 2 mv, it's nonnegotiable.

It must have momentum, and yet it has no kinetic energy...>>

All the kinetic energy is in the tennis ball; nothing is in the wall.

The wall has an infinitely large mass, but the momentum of this tennis ball has changed by an amount 2 mv.

**That momentum must be in the wall**--it's nonnegotiable, because momentum must be conserved.So now here you see in front of your eyes a case that the wall has momentum, but it has no kinetic energy.

That the wall has momentum 2 mv, it's nonnegotiable.

It must have momentum, and yet it has no kinetic energy...

How can that be? The wall is NOT moving, how can it has momentum?

I velocity for wall is zero, there is NO kinetic energy nor momentum, correct? But then why did he say that? Was it a trick question?