Collisions, Explosions and Impulse Flashcards
what does the momentum of an object depend on?
its mass and velocity
units of momentum
kgms-1
is momentum a scalar or vector?
vector so requires a direction
law of conservation of momentum
the total momentum before a collision is equal to the total momentum after a collision in the absence of external forces
law of conservation of energy
energy is always conserved
it cannot be created or destroyed
what may kinetic energy be converted into in a collision?
heat and sound
elastic collision
both momentum and kinetic energy are conserved
inelastic collision
only momentum is conserved, Ek is not
how to prove a collision is inelastic
Ek before>Ek after
if an object is travelling in the opposite direction what must you remember?
negative
impulse formulas
change in P=mv-mu
Ft=mv-mu
unit of impulse
Ns or Kgms-1
how to find impulse from a F-t graph
area under graph
what is the momentum normally before an explosion
0kgms-1
what happens if time of contact increase
average force exerted decreases
impulse stays the same so area under graph stays the same
what is conserved in all collisions
total energy
momentum gained by one object is equal to…
the momentum lost by the other
airbags
- safety feature in vehicles
- increase the time taken for a person’s head to decelerate to rest which therefore reduces the average force exerted on the person’s head
crumple zones
- safety feature at front and rear of vehicles
- increase time taken for vehicle to decelerate to rest on impact and therefore reduce the average force exerted on passengers.
