Pool Billiard can be viewed as elastic collision in 1D if balls are hit head on. Professional tables have balls of equal mass. What happens if the white ball

hits the 8 ball head on (ignore friction)? • White ball slows down, both balls move after collision• White ball stops, 8 ball moves with white ball’s velocity • White bounced back ( neg. velocity), 8 ball moves forward

slowly• White ball stops, 8 ball moves forward with less than

white ball’s velocity

Pool Billiard can be viewed as elastic collision in 1D if balls are hit head on. Bar tables have a heavier white ball.

What happens if the white ball hits the 8 ball head on (ignore friction)?

• White ball slows down, both balls move after collision• White ball stops, 8 ball moves with white ball’s velocity • White bounced back ( neg. velocity), 8 ball moves forward

slowly• White ball stops, 8 ball moves forward with less than

white ball’s velocity

• Choose your system• Is momentum conserved, i.e. are only internal forces

acting on the system’s constituents?• Draw two diagrams: initial and final situation• Choose a coordinate system, in particular + and –

directions• Apply monetum conservation equations• If elastic collision: apply kinetic energy conservation

equation• Solve for unknowns• Check results (reasonable?)

Collision Problem Solving

Example: Inelastic collision

• Two balls of clay with velocities v1 and v2 collide. After collision they are stuck together, what is their velocity?

Example: Elastic collision

• A white billiard ball of 100g and v=2m/s collides head-on with the 8-ball of 90g at rest.

• What are the velocities of the balls right after the collision?

Example: Collision in 2D

• Neutron hits Helium target elastically with v=6.2 10^5 m/s and Helium off at an angle of 45 degrees.

• What are the velocities (vectors!) of the protons after the collision?

A ladybug sits at the outer edge of a merry-go-round, and a gentleman bug

sits halfway between her and the axis of rotation. The merry-go-round makes a complete revolution once each second.

The gentleman bug’s angular speed is …• … half the ladybug’s. • … the same as the ladybug’s.• … twice the ladybug’s.• … impossible to determine.

A ladybug sits at the outer edge of a merry-go-round, that is turning and slowing down. The vector representing her angular velocity is in

the …

• -z direction• +z direction • +y direction • zero

z

x

y

A ladybug sits at the outer edge of a merry-go-round, that is turning and slowing down.

At the instant shown, the radial component of the bug’s (Cartesian) acceleration is in the …

• -x direction• +y direction • +z direction • Zero

z

x

y

A ladybug sits at the outer edge of a merry-go-round, that is turning and slowing down. At

the instant shown, the bug’s angular acceleration is in the …

• -z direction• -y direction • +y direction • +z direction

z

x

y

A ladybug sits at the outer edge of a merry-go-round, that is turning and slowing down due to

a force exerted on its edge. At the instant shown, the torque on the disc is pointing in …

• -z direction• -y direction • +y direction • +z direction

z

x

yF

A ladybug sits at the outer edge of a merry-go-round, that is turning and slowing down due to

a force exerted on its edge. The angular momentum of the bug is pointing in …

• -z direction• -y direction • +y direction • +z direction

z

x

yF

What is A x A ?

• Zero• A• -A• A2