Asked by anonymous
find the initial velocity of a .01 kg bullet that hits a 2 kg block and the block moves .1 meters.
Answers
Answered by
drwls
You need to know the force that stops the block from moving. Is it friction or is it mounted on a pendulum?
Answered by
anonymous
it's hanging from a string...
Answered by
Damon
Did anyone mention how long a string?
Conservation of momentum gives you the initial velocity v of the block with the bullet embedded as a function of bullet speed.
Then you can get the kinetic energy of that system at the impact from (1/2) m v^2
that becomes potential energy when the system stops.
That potential energy is m g h
where h is how much it went up
but how far it went up is
L ( 1-cos theta)
where theta is the angle of the string from vertical when it stops.
and we know that .1 = L theta where theta is in radians
In other words, I need L to do the problem.
Conservation of momentum gives you the initial velocity v of the block with the bullet embedded as a function of bullet speed.
Then you can get the kinetic energy of that system at the impact from (1/2) m v^2
that becomes potential energy when the system stops.
That potential energy is m g h
where h is how much it went up
but how far it went up is
L ( 1-cos theta)
where theta is the angle of the string from vertical when it stops.
and we know that .1 = L theta where theta is in radians
In other words, I need L to do the problem.
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