Topic 7 Flashcards
Definition: Impulse
The change of linear momentum, due to force x time.
(kgms⁻¹ or Ns)
Equation: Impulse *
FΔt = Δp
F = force (N)
Δt = time (s)
Δp = impulse ‘change in momentum’ (kgms-1)
How do crumple zones work?
They increase the time in which it takes the passenger to come to rest, reducing the force applied to the passengers.
How do you work out impulse from a force-time graph?
The area below the graph.
How do you solve a two-dimensional collision between objects?
1) Use a vector triangle.
2) Choose two perpendicular directions with the origin at the point of impact, and then use the conservation of momentum to solve the problem for each direction.
What is an elastic collision?
A collision between two objects where both kinetic energy and momentum are conserved.
What is an inelastic collision?
A collision between two objects where only momentum is conserved, kinetic energy is not.
What is the relationship between momentum and kinetic energy?
Ek = ½mv² = p² / 2m
How do you find out which type of collision has taken place?
Work out the initial Ek, and the total final Ek. If the initial Ek is equal to the total final Ek, then the collision is elastic, as Ek has been conserved.
What is a feature of all collisions?
Total energy is always conserved.
What type of collision has occurred when bodies stick together?
A totally inelastic collision.
Why does gun recoil when a bullet is fired from it?
1) According to Newton’s 3rd Law every action has an equal and opposite reaction so the bullet and gun exert an equal and opposite force on each other.
2) For momentum to be conserved they must travel in an opposite direction as the initial momentum is zero.
3) Because the gun has a larger mass, it will have a lower velocity so not move as far.
