Momentum & Impulse
Conservation of momentum, impulse-momentum theorem
Momentum and Impulse
Momentum: p = mv (kg.m/s). Impulse: F delta t = delta p = mv_f - mv_i. Conservation of momentum: in an isolated system, total momentum before equals total momentum after a collision.
Example
Worked Example
A 2 kg ball at 5 m/s right collides with a 3 kg ball at rest. After collision the 2 kg ball moves at 1 m/s right. p_before = 10 kg.m/s. p_after: 2(1) + 3(v2) = 10. v2 = 2.67 m/s right.
Note
Exam Tip
Define positive direction. Momentum is a vector — direction matters. Airbags and crumple zones increase collision time (delta t), reducing force (F) on passengers.
Key Vocabulary
MomentumThe product of mass and velocity of an object (p = mv)
ImpulseThe product of net force and time, equal to change in momentum
Conservation of momentumTotal momentum before equals total momentum after in an isolated system
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Momentum
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