Mechanics > Linear Momentum > Conservation DCS# 1M40.40
SPEED OF BULLET

APPARATUS
toy rifle on wooden mount 202-14-F
bullet 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
Use the video or Powerpoint version of this demo.  A non-functional toy rifle version is available to show the setup.  Here is a description of how the demo has been performed in the past:

Fire a bullet into a hanging wooden block.  Compare the measured speed to that determined using conservation of momentum.

The bullet passes through two foil triggers connected to the storage scope.  The initial speed of the bullet can be calculated from their separation and the time between the pulses.

A flag attached to the bottom of the block passes through a photogate.  The post-collision speed of the block+bullet can be found from the width of the flag and the time the photogate is blocked.
NOTES
 
Data:
mass of lead part of bullet, m 2.6 g
mass of block, M  3.0 kg
distance between foil triggers, x1
 1.00 m
expected time of flight, t1 5.8 ms
width of flag through photogate, x2 3.0 cm
expected time photogate blocked, t2 0.19 s
Setup:
    Clamp the wooden gun mount to the demonstration bench, keeping clamps clear of the chalkboards.

    Clean rifle bore with kit 202-14-F.

    Hang the block from the unistrut grid in the ceiling.  The strings will stretch, so level the block just prior to the demo.
     
    Assemble the 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 the trigger circuit.

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

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

    Hang paper from a ringstand just past the end of the 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