1. Conservation of Momentum Representations
Unit 9
Conservation of Momentum Representations

2. What geometric shape could represent momentum? (p = m*v)
How would it change for objects of various masses, velocities and positive and negative directions?

3. Example 1
A 40 kg girl rollerblades at 4 m/s toward her 20 kg dog, who is running at 7 m/s in the opposite direction. The dog leaps into the girl’s arms and they continue rolling together. Determine their velocity.

4. object/mass/velocity– +
final
object/mass/velocity
initial
event: dog leaps into girls arms(stickie)

5. object/mass/velocity– +
final
object/mass/velocity
initial
event: dog leaps into girls arms(stickie)
40 kg
60 kg
20 kg
-7 m/s
+4 m/s
? m/s
pgi = mgvig = 40 kg*4m/s = 160 kgm/s
pdi = mdvid = 20 kg*-7m/s = -140 kgm/s
ptotal = 160 kgm/s kgm/s = 20 kgm/s
60kg * vf

6. Example 2
A 0.03 kg bullet travelling at 300 m/s ricochets off a 500 kg smart car, in neutral at rest, at 100 m/s in the opposite direction. Determine the momentum transferred to the car.

7. object/mass/velocity– +
final
object/mass/velocity
initial
event: bullet bounces off car (bouncie)

8. object/mass/velocity– +
final
object/mass/velocity
initial
event: : bullet bounces off car (bouncie)
0.03 kg
0.03 kg
500 kg
500 kg
0 m/s
+300 m/s
-100 m/s
? m/s
pbi = mbvib = 0.03 kg*+300m/s = 9 kgm/s
pbf = mbvfb = 0.03 kg*+-100m/s = -3 kgm/s
pci = mcvic = 500 kg*0m/s = 0 kgm/s
pcf = +12 kgm/s
ptotal = 9 kgm/s + -0 kgm/s = 9 kgm/s