**Conservation of Momentum** (demonstration)

**Obj:** Determine the muzzle velocity of a BB and the recoil velocity of
a BB gun using the LCM.

**Equipment:**
Air Track, BB Gun, balance,* *photogate, goggles

**Methods:**

1.
Sketch the set-up.

2. Determine the
average mass of one BB (m_{b})_{.}

3. Mass the glider
(m_{g}) with the clay, and the gun (m_{n})_{.}

4. Determine the
length of the timing card.

5.
Shoot the BB into the clay of the glider.

6. Record the time
the glider takes to travel the length of the card.

7. Repeat for 4
other trials and average the times.

**Analysis**

1.
Using the LCM, calculate the average BB velocity (m_{b}v_{b}
= m_{g}v_{g})

2.
Calculate the average recoil velocity of the gun using the
momentum of the BB or the glider (m_{n}v_{n} = m_{b}v_{b}
= m_{n}v_{n})

3.
Why was the mass of the BB ignored in the calculations?

4.
How long would it take the BB to travel one football
field, 100 m long?

5. If the gun was
fired horizontally 1.50 m above the ground, what is the
horizontal range of this BB gun?
Is there enough time to travel one football field (see
answer in No. 4)?

6. What was the
momentum of the system before and after firing?
Explain.

7.
State the LCM in words.

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