1. Unit 5: Momentum
Lesson 3: Collisions

2. Conservation of Momentum
During a collision, total momentum is conserved!
In equation form: p1b + p2b = p1a + p2a
(This assumes there are NO OUTSIDE FORCES.)
5 min

3. Collision Problems p before = p after mgvg + 0 = mgmvgm
Example 1: A 4000 kg garbage truck going 72 km/h collides with a stationary Mini of mass 900 kg. They stick together just after the collision. Find the velocity of the combined wreckage.
10 min
p before = p after
mgvg + 0 = mgmvgm
(4000)(72/3.6) = ( )v
v = 16.3 m/s
= 59 km/h

4. p before = p after (800)(33.3) + (1400)(-13.9) = 2200v v = 3.26 m/s
Example 2 (Try it!): A 1400 kg PT Cruiser going 50 km/h West collides head-on with a 800 kg VW Beetle going East at 120 km/h. If they stick together, find the final velocity.
(50 km/h)/3.6 = 13.9 m/s
15 min
(120 km/h)/3.6 = 33.3 m/s
p before = p after
(800)(33.3) + (1400)(-13.9) = 2200v
v = 3.26 m/s
= 12 km/h East

5. Brain Break!

6. Example 3 (Try it!): A 1700 kg truck collides head-on with a 68 tonne tank going West at 15 m/s. The wreckage sticks together and moves West at 13.5 m/s just after the collision. Find the initial velocity of the truck. ?
15 m/s
13.5 m/s
15 min
p before = p after
1700v (-15) = ( )(-13.5)
1700v = 68000(15) (-13.5)
v = 46.5 m/s or 167 km/h

7. Homework
Pg. 125 #1-3 and pg. 126 #4 and 6
10 min

8. Lesson 4: More Collisions
Unit 5: Momentum
Lesson 4: More Collisions

9. Example 4: A 250 g pool ball going 1
Example 4: A 250 g pool ball going 1.7 m/s strikes a stationary 320 g ball which bounces forwards at 0.80 m/s. Find the velocity of the first ball just after the collision.
before
after ?
10 min
p before = p after
(0.25)(+1.7) + 0 = .25v + (0.32)(+0.8)
.25v = -(0.32)(+0.8) + (0.25)(+1.7)
v = m/s

10. ? p before = p after (7500+1200)v = 7500(24) + 1200(62) 8700v = 254400
Example 5 (Try it!): A 7500 kg spaceship deploys a 1200 kg satellite at 62 m/s forwards. The final velocity of the ship is 24 m/s forwards. Find the initial velocity.
before
after ?
p before = p after
( )v = 7500(24) (62)
8700v =
v = 29.2 m/s forwards
15 min

11. Brain Break!

12. Practice Time!
Do Collision Problems #1-6