📚 Topic Summary
Inelastic collisions are collisions where kinetic energy is not conserved. This means some of the energy is converted into other forms, such as heat or sound. A classic example is a car crash. The key characteristic of inelastic collisions is that the objects involved stick together or deform during the collision. To solve inelastic collision problems, we primarily use the conservation of momentum principle. Remember that momentum is always conserved in collisions, regardless of whether they are elastic or inelastic!
The formula for conservation of momentum in an inelastic collision is: $m_1v_{1i} + m_2v_{2i} = (m_1 + m_2)v_f$, where $m_1$ and $m_2$ are the masses of the objects, $v_{1i}$ and $v_{2i}$ are their initial velocities, and $v_f$ is the final velocity of the combined mass.
🧠 Part A: Vocabulary
Match the terms with their definitions:
| Term |
Definition |
| 1. Kinetic Energy |
A. A collision where kinetic energy is not conserved. |
| 2. Momentum |
B. The energy of motion. |
| 3. Inelastic Collision |
C. A measure of an object's mass and velocity. |
| 4. Conservation of Momentum |
D. The total momentum of a closed system remains constant. |
| 5. Velocity |
E. The speed of an object in a given direction. |
Match the correct Definition with the Term.
1 - B
2 - C
3 - A
4 - D
5 - E
✍️ Part B: Fill in the Blanks
In an inelastic collision, ______ energy is not conserved. Instead, some of the energy transforms into other forms, such as _____ or _____. However, the total ______ of the system is always conserved. This principle allows us to analyze and solve problems involving inelastic collisions using the formula: $m_1v_{1i} + m_2v_{2i} = (m_1 + m_2)v_f$. In these types of problems, objects often ______ together after impact.
Answer:
Kinetic, heat, sound, momentum, stick
🤔 Part C: Critical Thinking
Explain, in your own words, why momentum is always conserved in collisions (both elastic and inelastic), even though kinetic energy might not be.
Answer:
Momentum conservation stems from Newton's Third Law (action-reaction pairs). During a collision, the forces between objects are internal to the system. These internal forces cause changes in momentum for each object, but because they are equal and opposite, the total momentum of the system remains constant. Kinetic energy, on the other hand, can be converted to other forms of energy (heat, sound, deformation) during the collision, violating its conservation.