Dynamics

Conservation (No Collision)

AP Momentum

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Conservation of Momentum – No Collision — total momentum before an interaction equals total momentum after, even when the objects never collide (a load dropped onto a car, a particle emitted from a nucleus).

Ex 1) Railroad Car

A 12,600 kg railroad car travels on a frictionless surface with a constant speed of 18.0 m/s. A 5350 kg load at rest is dropped onto the car, what will the car’s new speed be?

Total momentum before = total momentum after

m1v1 = m2v2

↓

V2 = 12.6 m/s

Ex 2) Alpha Particle Emission

Ex) An atomic nucleus moving at 420 m/s emits an alpha particle in the direction of its motion and the remaining nucleus slows to 350 m/s.

If the alpha particle has a mass of 4.0 µ and the original nucleus has a mass of 222 µ, what speed does the original alpha particle have when it is emitted?

No need to convert mass to kg. Why?

Before

Original nucleus mass = 222 µ,

v = 420 m/s

After

Alpha particle mass = 4.0 µ

v = ?

New Nucleus = 218 µ (alpha lost)

v = 350 m/s

Speed of original alpha particle when it is emitted?

mom nucleus = mom alpha + mom new nucleus

mv = mava + mnvn

↓

v = 4.2 × 103 m/s

Related

Recoil Problems

Recoil Problems

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