01 Key Concepts
Momentum Definition
p = m*v, the product of an object's mass and velocity; like velocity, momentum is a vector quantity.
Units of Momentum
Measured in kg*m/s (there's no separate named unit).
Conservation of Momentum
In a closed system with no external forces, total momentum before a collision or interaction equals total momentum after.
Elastic vs. Inelastic Collisions
In an elastic collision, both momentum AND kinetic energy are conserved. In an inelastic collision, momentum is conserved but some kinetic energy converts to other forms (like heat or sound).
Perfectly Inelastic Collisions
A special case where the colliding objects stick together and move with a common final velocity after impact.
02 Key Formulas
- p = m*v
- Conservation: m1*v1 + m2*v2 = m1*v1' + m2*v2'
03 Solved Examples
Example 1 Find the momentum of a 5 kg object moving at 8 m/s.
- Apply p = m*v = 5*8.
Answer: 40 kg*m/s
Example 2 A 2 kg ball moving at 6 m/s collides with a stationary 4 kg ball, and they stick together. Find their common velocity after collision.
- Total momentum before = total momentum after (conservation).
- Before: (2*6) + (4*0) = 12.
- After: (2+4)*v = 6v.
- Set equal: 12 = 6v, so v = 2.
Answer: 2 m/s
Example 3 Is a collision where two cars crash and crumple together (sticking) elastic or inelastic?
- Objects sticking together after collision, moving with a shared velocity, is the defining feature of a specific collision type.
Answer: Perfectly inelastic
04 Practice Questions
1Find momentum of a 3 kg object at 10 m/s.
30 kg*m/s
2Find momentum of a 10 kg object at 2 m/s.
20 kg*m/s
3A 1 kg ball at 5 m/s hits a stationary 1 kg ball and they stick. Find final velocity.
2.5 m/s (using conservation: 5=2v)
4Is momentum a scalar or vector?
Vector
5What is conserved in ALL types of collisions (elastic and inelastic)?
Total momentum
📄 Momentum — Downloadable Worksheet
10 questions with a full answer key. Grab the PDF to print, or try the interactive version in your browser.