applying a force. impulse momentum conservation of momentum collisions momentum
TRANSCRIPT
Applying a Force
ImpulseMomentum
Conservation of MomentumCollisions
Momentum
ImpulseThe product of force and contact time
Vector quantity, Symbol: JDirection is the same as the net or
average force appliedUnits: N-s, kg-m-s-1
Momentum
Product of mass and velocityVector quantity, Symbol: p
Direction is the same as the velocity
Units: kg-m-s-1
Large Force, Short Contact Time
Can you give other examples?
Small Force, Long Contact TimeAirbags
Seatbelt
Small Force, Long Contact TimeCatching a baseball
Bungee Jumping
Example
A cricket ball, mass 0.5 kg, was bowled at50 m s-1 at a batsman who misreads theball and the 5 kg bat is knocked out ofhis hands, the ball rebounds at 25 ms-1.
What is the change in momentum of the ball?If the bat was in contact with the ball for 2.0
ms, how much force did the batsman apply on the ball?
Conservation of Momentum
Total momentum before is equal to total momentum after
In a closed system (external forces are negligible)
Inelastic CollisionOnly momentum is conserved
Perfectly inelastic collision(The colliding bodies couple after
the collision)
Example
A railway wagon travelling at 1.0 m s–1 catches up with and becomes coupled to another wagon travelling at 0.5 m s–1 in the same direction. The faster moving wagon has 1.7 times the mass of the slower one. Immediately after impact, what is the speed of the coupled wagons?
Elastic Collision
Momentum is conserved.Kinetic Energies are conserved.
(Relative Velocities) are conserved.Analyzing billiard balls
Simulation
ExampleA trolley of mass 1 kg rolls along a level,
frictionless ramp at a speed of 6 m s-1. It collides with a second trolley of mass 2 kg which is initially at rest. The first trolley rebounds at a speed of 2 m s-1.Find, by conservation of momentum, the
velocity of the second trolley after the collision.
Compare the kinetic energy before and after the collision. Is the collision elastic?
ExampleA ball of mass 0.20 kg is dropped from a
height of 3.2 m onto a flat surface which it hits at 8.0 m s-1. It rebounds to 1.8 m. (g = 9.8 m s-2)What is the rebound speed just after impact?What is the change in energy of the ball?What momentum change has the ball between
just touching the surface and leaving it?
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