The ballistic pendulum consists of a suspended block which is struck by a fast-moving projectile. It is an example of "combined mechanics" meaning that it involves physics concepts from a range of topics.
The topics are:
conservation of momentum (when the slug hits the block)
conservation of energy (when the block rises up after being struck by the slug).
Data collected by 12PHYMC classes:
Mass of slug = 0.50g
Mass of block = 252.0g
Height change of block after being struck = 6.0mm.
Calculations
As the block moves upwards, kinetic energy is converted to potential energy
½mv²=mg∆h
=> v=√(2g∆h)
=> v=√(2*10*0.006)=0.3464m/s
So we now know the block had momentum immediately after being struck of 0.2525*0.3464=0.08747kgm/s.
As the block had no momentum before being struck, this must also be the momentum of the slug immediately before it hit the block.
So now we can work out the size of the slug's velocity:
ρ=mv
=>v=ρ/m=0.08747/0.00050=174.9m/s (170m/s to 2 sf)
Ballistic pendulum
Video sent by johnmc2
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