Mechanics > Linear Momentum > Conservation DCS# 1M40.40
SPEED OF BULLET
APPARATUS
rifle on wooden mount 202-14-F
bullets 202-14-F
wooden block 202-14-F
photogate 202-14-B2
storage scope 202-08-B
two foil triggers 202-14-F
two power supplies 202-08-D
two 500 k resistors 107
two 100 ohm resistors 101-09-I6
two 0.5 uF capacitors 101-09-G4
two key switches 101-09-D4
DESCRIPTION
Fire bullet into hanging wooden block.  Compare measured speed to that predicted by conservation of momentum.

Determine intial speed of bullet by the following methods:

1.  Bullet passes through two foil triggers connected to the storage scope.  Calculate v from their separation and the time between the pulses.  Speed should be about 330 m/s.

2.  Find final speed of bullet+block by one of the methods described below and apply conservation of momentum.  Final speed of system should be about 0.2 m/s.

a.  Flag attached to the bottom of the block passes through a photogate.  Calculate V from width of flag and time photogate is blocked.

b.  Block can be made to slide a marker along a meterstick as it swings back.  Height block rises can be calculated and conservation of energy applied.
NOTES
 
Data:
mass of lead part of bullet, m 2.6 g
mass of block, M  2.972 kg
distance between foil triggers, d 1.00 m
expected time of flight, t (3.0 ms)
width of flag through photogate, x 3.1 cm
expected time photogate blocked, t2 (0.15 s)
Setup:
    Clamp wooden gun mount to demonstration bench, keeping clamps clear of chalkboards.

    Clean rifle bore with kit 202-14-F.

    Hook block to wires hanging from ceiling.  Wires will stretch, so level the block just prior to demo.
     
    Assemble foil triggers as shown below, making sure there is no contact between the two pieces of foil.  Set them 1.00 m apart.  Use key switches to test trigger circuit.

    Use "gate" setting on photogate.  Check that flag passes through squarely.

    To check mass of bullets, empty powder from case and weigh only lead part.  Keep bullets locked away until ready for use.

    Hang paper from ringstand just past end of gun to catch powder.

Triggers:
    Switches closed by passage of bullet:

    Circuit for producing pulse on scope:
    Scope settings:
    ch1, 2:  5 V/div
    sweep rate:  1 ms/div
    trigger on + slope
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