Physics Chap 7

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Kinetic Energy conservation equation

1/2m₁v² =1/2m₁Vf₁² + 1/2m₂Vf₂²

Impulse equation

F ∆t

Other equation for change in momentum

F∆t = m∆v

Big Idea

Momentum is conserved in all collisions, as long as external forces do not act

Momentum conservation equation

P total = m₁v₁ +m₂v₂

Total momentum

Ptotal = p₁ + p₂ + ...

Two dimension collision equations

Px₁ = Px₂ Py₁ = Py₂

Elastic collision in one dimension, when m₁ is moving with an initial velocity of v and m₂ is initially at rest. The velocities of the masses after the collision is seen with this equation (Vf₁)

Vf₁ = ((m₁-m₂) / (m₁+m₂)) *v

Elastic collision in one dimension, when m₁ is moving with an initial velocity of v and m₂ is initially at rest. The velocities of the masses after the collision is seen with this equation (Vf₂)

Vf₂ = ((2m₁)/(m₁+m₂)) *v

Momentum conservation applies to ______ collisions.

all

if the velocity changes direction, the momentum does what?

also changes direction

Only ______ forces can change a system's momentum

external

Internal force

forces acting between objects within the system

External forces

forces exerted on a system by something outside of the system

Conservation of momentum

if the total force acting on an object is zero, its momentum cannot change. p₁ = p₁

Recoil

is a result of momentum conservation

A railroad car of mass m moving with speed v collides and stick to an identical railroad car that is initially at rest. After the collision what is the final kinetic energy compared to the initial?

it is one-half the initial kinetic energy

Si unit for impulse

kg * m/s

Units of momentum

kg * m/s

Elastic Collision

kinetic energy is conserved (KE₂ = KE₁)

Inelastic collision

kinetic energy is not conserved, (total energy is conserved, but just transformed to other forms)

Magnitude of momentumequation

mv (mass *speed)

Momentum equation

mv (mass* velocity)

Impulse shows what?

the change in the object's momentum

What determines the direction of an impulse?

the force

Total momentum of a system is the _______ (2) of the momentums of all the individual objects.

vector sum

Completely inelastic collision

when the objects stick together

Momentum can be resolved into its ______.

x and y components

Impulse equation (in terms of momentum)

∆p (p₂ - p₁)

Change in momentum equation

∆p = p₂ - p₁

F total = ?

∑F external


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