ELASTIC & INELASTIC

Analyzing Collisions

Collisions

During a collision, there is a transfer of momentum & energy.

To calculate momentum =pai + pbi = paf + pbf

(remember p = mΔv)

To calculate energy =KEai + KEbi = KEaf + KEbf (remember KE = ½ mv2)

Collisions

2 types of collisions#1 = Elastic – “hit & rebound”

- momentum is conserved For Perfectly Elastic- KE remains the same

ma

va initial

mb

vb initial

P before = ma(+va) + mb(-vb)

mb

vb final

P after = ma(-va) + mb(+vb)

ma

va final

Elastic Collision Equation

ma(+va) + mb(-vb) = ma(-va) + mb(+vb)

*Positive velocity to the right*Negative velocity to the left

Collisions

2 types of collisions#2 = Inelastic – “hit & stick”

- momentum is conserved For Perfectly Inelastic- KE is decreased

Collision: hit and stick

ma

va initial

mb

vb initial

P before = ma(+va) + mb(-vb)

mb

vb final

P after = (ma + mb)(va&b

combined)

ma

va final

vab

Collision: hit and stick

Inelastic Collision Equation

ma(+va) + mb(-vb) = (ma + mb)(va&b

combined)

*Positive velocity to the right*Negative velocity to the left