Cards In This Deck

• $\text{First step to solve any collision problem involving two particles?}$
  $\text{Draw a diagram showing velocities before and after impact, and explicitly define a positive direction (e.g., with an arrow }\to \text{).}$
• $\text{Condition for the Principle of Conservation of Momentum (}{m}_1{u}_1+m_2{u}_2=m_1{v}_1+m_2{v}_2\text{) to be valid?}$
  $\text{There must be no external forces acting on the system along the line of motion (e.g., no friction or air resistance).}$
• $$\begin{gathered} \text{True or False? } \\ \text{In a collision, if you don’t know the direction a particle moves after impact, you should assume it stops.} \end{gathered}$$
  $$\begin{gathered} \text{❌ False} \\ \text{Assume it moves in the positive direction with velocity }v\text{. Calculate }v\text{. If the result is negative, it actually moves in the opposite direction.} \end{gathered}$$
• $\text{Two particles connected by a slack string move apart. How do you find the common speed immediately after the string becomes taut?}$
  $\text{Apply Conservation of Momentum to the combined system of both particles.}$
• $$\begin{gathered} \text{True or False? } \\ \text{When Particle A collides with Particle B, the impulse exerted by A on B is larger if A is much heavier than B.} \end{gathered}$$
  $$\begin{gathered} \text{❌ False} \\ \text{By Newton’s 3rd Law, the impulses are equal in magnitude and opposite in direction (}{I}_{AB}=-I_{BA}\text{), regardless of mass.} \end{gathered}$$