(L9) Mechanics 5 - Momentum Flashcards
What is momentum equation?
p=mv
What is N’s 2nd law?
F=ma
“The (time) rate of change of momentum is proportional to the net external force”
What is impulse equation?
F∆t = ∆p
What is momentum like during a collision?
p,net = 0.
forces are opposite and equal. symmetrically invserse. due to N’3 rd law.
provided no net external forces
What are inelastic conditions?
Momentum is conserved (as long as no external forces)
Kinetic energy is not conserved (some is converted to heat or sound)
What are elastic conditions?
Momentum is conserved (as long as no external forces)
Kinetic energy is conserved
Solving collision problem steps
- define system of interest, incl. forces
- draw system before and after collision
- decide on coordiante origin and decide pos/neg (if in 2d break into vector components)
- is collision elastic/inelastic? do components stick together?
What is a ‘totally’ inelastic collision?
If colliding objects are sticky and inelastic, so they stick together after they’ve collided.
before: m1v1+m2v2 after: m1+m2*v,f
momentum conserved but inelastic so KE not conserved
How can we relate kinetic energy and momentum in an equtiton?
How can we combine the kinetic energy and momentum equation?
“The relative speed of the objects before the collision
equals the negative of their relative speed after the
collision”
What occurs in momentum = 0?
Collision may still occur. ek conserved, p conserved. so elastic
What’s velocity like of elastic collisions?
Elastic collisions: relative velocity before = −relative velocity after
What happens to KE when a ball hits a heavy object?
A tiny little bit of the kinetic energy will be transferred too the other object.
