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AP Physics – Conservation of Momentum
AP Physics – Conservation of Momentum
Momentum is Conserved in all collisions in isolated system -- no external forces acting
Momentum before = momentum after
Elastic collision ( kinetic energy is conserved
Inelastic collision ( kinetic energy is not conserved
Perfectly inelastic collision ( object stick together and have same velocity.
15 000 kg Railroad car moving at 2.5 m/s collides and couples with stationary 12 500 kg car. What is new velocity of the two cars?
2 mud balls collide in a perfectly elastic collision. One has a mass of 4.0 kg, the second has a mass of 3.5 kg. The first one has a velocity of 3.4 m/s, the second has a velocity of – 4.8 m/s. What is their velocity after the collision?
Head on Collisions:
Momentum and KE are conserved
Cancel out the ?
Recombine things to get the m’s together
Factor things out:
Back to momentum:
Put the m’s together:
Now divide the 2 equations that we got into each other:
Two balls collide as shown, what is their final velocity?
since the 2 masses are equal, they cancel out.
Observe:
solve for a final velocity:
Plug into other equation:
EQN: get:
Clean up:
More Algebra:
get
So the 2 balls exchange velocities.
Balls hit head on as shown, what is their final v?
Solve for v2f:
Plug into other equation:
Solve for v1f :
stick on other side of = :
Group v’s:
Factor out the v:
Plug and chug:
Solve for other v :
New Problem:
plug in value
Newton’s Cradle Demo
Dropping balls
Glancing collisions:
An 8.00 kg mass moving east at 15.0 m/s strikes a 10.0 kg mass that is at rest. The 8.00 kg mass ends up going south at 4.00 m/s. What is the velocity of the second ball? What percent of the KE is lost in the collision?
= 12 m/s
AP Test Question:
Two identical objects A and B of mass M move on a one-dimensional, horizontal air track. Object B initially moves to the right with speed vo. Object A initially moves to the right with speed 3vo, so that it collides wi
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