Collisions

Question 1

Centre of Mass Velocity Equation

Answer 1

(m1 v1 + m2 v2) / (m1 + m2)

Question 2

CoM Velocity to Lab Frame Velocities

Answer 2

u = u’ + vcm

‘ is velocity in CoM frame

Question 3

Is vcm changed or unchanged by a collision

Answer 3

vcm is unchanged by a collision

Question 4

Completely Inelastic Collision

Answer 4

• The 2 particles stick together
• q1’ = q2’ = 0
• All KE is lost in the CoM frame (Not lab frame)
• In lab frame, final velocity is the vcm

Question 5

Elastic Collision

Answer 5

• Initial and Final momentum have same magnitude in CoM frame
• After collision, speeds are in opposite directions

Question 6

Inelastic Collision Question Walkthrough

Answer 6

• Find vcm
• Final velocties = 0 in CoM frame
• Final velocities = vcm in lab frame

Question 7

Elastic Collision Question Walkthrough

Answer 7

• Find vcm
• Find Initial speeds in CoM frame
• Flip signs
• Turn inital speeds to lab frame speeds