Physics / Unit 6: Momentum and Collisions
6.1 Momentum
Notes
Momentum is mass in motion: $p = mv$. It is a vector that points in the direction of the velocity.
- Unit: $\text{kg·m/s}$.
- A slow, heavy object can have the same momentum as a fast, light one.
- Direction matters: pick a positive direction; momentum the other way is negative.
- Example: a 0.5 kg ball moving at $8 \text{ m/s}$ has $p = 0.5 \times 8 = 4 \text{ kg·m/s}$.
Practice
What is the momentum of a 70 kg runner moving at $5 \text{ m/s}$?
$p = 70 \times 5 = 350 \text{ kg·m/s}$.
Which has the most momentum?
Momenta: 10, 16, 12 and $0 \text{ kg·m/s}$.
A 1,200 kg car has a momentum of $18000 \text{ kg·m/s}$. What is its speed?
$\displaystyle v = \frac{p}{m} = \frac{18000}{1200} = 15 \text{ m/s}$.
Ready for more? Take the Unit 6 test.