AP Physics
Conservation of Momentum
Head on Elastic Collisions
Elastic Collision?
No energy lost in collision
(1/2)m1v12 + (1/2)m2v22 =
(1/2)m1v1f2 + (1/2)m2v2f2
Combine equations above with
m1v1 + m2v2 = m1v1' + m2v2'
you get .....
For Head-on Collisions:
V1 - V2 = V2' - V1'
↓ Scroll for Problem 1 ↓
Giancoli - page 189) 23
m1 = .450 kg
V1 = 3.00 m/s
m2 = .900 kg
V2 = 0
↓ Scroll for Step 1 ↓
V1 - V2 = V2' - V1'
V2' - V1' = 3 m/s
V2' = 3 m/s + V1'
↓ Scroll for Step 2 ↓
Total Mom before = Total Mom After
1.35 kgm/s = .45V1' + .90kg(3 + V1')
1.35 = 1.35V1' + 2.7
V1' = -1 m/s (or 1 m/s West)
↓ Scroll for Final Step ↓
Since
V2' = 3 m/s + V1'
then ...
V2' = 2 m/s East
Collisions in 2 Dimensions
Momentum is conserved
in x and y directions
Total Mom in X direction before =
Total Mom in X direction after
Total Mom in Y direction before =
Total Mom in Y direction after
If angle between = 90 degrees ...
Add vectors using ....
a2 + b2 = c2
Textbook - p. 190) 41
Total Momentum Before
↓ Scroll for Step 1 ↓
Eagle 1:
mv = 4.3 kg(7.8 m/s)
= 34 kgm/s
Eagle 2:
mv = 5.6 kg(10.2 m/s)
= 57 kgm/s
↓ Scroll for Step 2 ↓
Total Mom before:
a2 + b2 = c2
342 + 572 = c2
Total mom before = 66 kgm/s
↓ Scroll for Final Answer ↓
66 kgm/s = (5.6kg + 4.3kg)v
V = 6.7 m/s
problem 42)
Gravity, Friction Momentum
Chapter Review
Enrichment
Rifle Recoil
Dr. Dave's Hall of Fame
Established 1995
Use any material on this site (w/ attribution)