2D Collisions and Center of mass 1

Collisions or Explosions in Two Dimensions y x after before Ptotal,x and Ptotal,y independently conserved Ptotal,x,before = Ptotal,x,after Ptotal,y,before = Ptotal,y,after 37

Example: shooting pool during before after pf F vo = 3m/s vcm At rest 300 Mass of both balls is 2kg vf =2m/s Find final velocity and direction of white ball vf =2m/s 43

Example: shooting pool (cont.)

Center of Mass Some objects can’t be balanced on a single point Center of Mass = Balance point Some objects can’t be balanced on a single point 46

Example: center of mass m = 0.140 kg 0.1m M = 0.515

Velocity of Center of Mass The speed of the balance point 46

Elastic Collisions Find Vcm. Subtract Vcm from both initial velocities. Change sign of both velocities. Add Vcm to both velocities.

Example: collision “before” “after” Vo = 3m/s Vo = 0m/s M1=2kg M1=2kg M2=1kg M2=1kg Two blocks collide and bounce apart, what is their final velocity?

Example: collision “before” “after” Vo = 3m/s Vo = 3m/s M1=2kg M1=2kg M2=1kg M2=1kg Two blocks collide and bounce apart, what is their final velocity?

Summary Collisions and Explosions Center of Mass (Balance Point) Draw “before”, “after” Define system so that Fext = 0 Set up axes Compute Ptotal “before” Compute Ptotal “after” Set them equal to each other Center of Mass (Balance Point) 50