6 collisions

impulse

• product of avg force acting on body and time fort which it acts on body

• Ft = change in p = area under Ft graph

principle conservation of linear momentum

total linear momentum in a system in constant provided no ext force acts on the system

• no change in p

types of collision

1. elastic

• KE conserved, relative speed of approach = relative speed of separation

  • Ua - Ub = Vb - Va

• head on collision: bodies move off in a straight line connecting the 2 bodies’ centre of mass after colliding

2. inelastic collision

• KE not conserved, but p is

• perfectly inelastic: bodies will coalesce/stick tgt after colliding

3. special cases of 1D collision

• m1=m2

  • exchange velos

• m1 » m2

  • m1: vlelo approximately unchanged

  • m2: rebounds with approx 2x the velocity of m1

• m1 « m2

  • m1: velo approx reversed

  • m2: approx at rest

is collision elastic?

1. 1 direction

• RSOA = x

• RSOS = y

• since x=y, KE conserved, collision elastic

2. >1 direction

• KEi = x

• KEf = y

• since x=y, KE conserved, collision elastic

can 2 bodies be at rest simultaneously?

1. find TPi

2. since p must be conserved given that no net ext force acts on it, Pi=Pf

3. since TPi is nonzero, TPf shd also be nonzero

4. hence both bodies cannot be at rest simultaneously