Momentum
Momentum
- Momentum = mass × velocity (a vector).
- In a collision, total momentum is conserved:
$$m_1 u_1 + m_2 u_2 = m_1 v_1 + m_2 v_2$$
- Example: a 2 kg body at 3 m/s hits a stationary 1 kg body and they stick: $2(3) + 1(0) = 3v$, so $v = 2\,\text{m s}^{-1}$.
Practice
A 2 kg body moving at 3 m/s hits a stationary 1 kg body and they stick together. What is their common speed (m/s)?
2(3) + 1(0) = (2+1)v, so 6 = 3v, giving v = 2 m/s.
Practice
Momentum is defined as:
Momentum = mass × velocity, a vector quantity.
Practice
In a collision, the total momentum of the two bodies is conserved.
Total momentum before equals total momentum after the collision.
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Key idea
- momentum = mass × velocity (a vector)
- conservation: $m_1 u_1 + m_2 u_2 = m_1 v_1 + m_2 v_2$
- total momentum is the same before and after a collision