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PRACTICE · MEMBERSIntermediate · Single correct

PRACTICE / Motion of the center of mass

Follow the system, not either cart

Two carts of masses 2 kg and 3 kg initially move at +4 m/s and −1 m/s on a frictionless horizontal track. A mechanism between them later changes their individual velocities using internal forces only.

What is their center-of-mass velocity throughout this interaction?

Organize the givens & assumptions
  • m₁ = 2 kg, v₁ = +4 m/s
  • m₂ = 3 kg, v₂ = −1 m/s

No external horizontal force; fixed total mass; the mechanism’s mass is negligible and included in the system.

  1. A+2.2 m/s+2.2\ \mathrm{m/s}
  2. B0 m/s0\ \mathrm{m/s}
  3. C+1 m/s+1\ \mathrm{m/s}
  4. D+1.5 m/s+1.5\ \mathrm{m/s}

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