Conservation of Momentum Practice
1. You (60kg) and you beau (45kg) are at an ice rink holding hands. You start at
rest facing each other, and push apart, going off in opposite directions. If your
velocity is 3m/s, what is the velocity of your beau?
Before:
After:

Before: 0 m/s  

After: -4 m/s

Explanation:

Before: Since you and your beau started at rest, your beau initial velocity is 0 m/s.

After: Since we have to conserve momentum,

momentum before push = momentum after push.

The momentum before push = 0 (since you and your beau are at rest)

momentum after push = m₁v₁ + m₂v₂ were m₁ = your mass = 60 kg, v₁ = your velocity after push = 3 m/s, m₂ = beau's mass = 45 kg and v₂ = beau's velocity.

So, m₁v₁ + m₂v₂ = 0

m₁v₁ = -m₂v₂

v₂ = -m₁v₁/m₂ = -60 kg × 3 m/s ÷ 45 kg = -4 m/s

So beau moves with a velocity of 4 m/s in the opposite direction

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