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Two identical objects have a one-dimensional collision in which one is initially motionless. After the collision, the moving object is found to be stationary and the other moves off with exactly the speed the first one originally had. What kind of collision is this?
AAn impossible result that violates conservation of momentum
BA perfectly inelastic collision, since the objects end up moving at different speeds
CAn elastic collision, since it satisfies both momentum and kinetic energy conservation
DA collision in which kinetic energy always must be lost here
Answer & Solution
Correct answer: C. An elastic collision, since it satisfies both momentum and kinetic energy conservation
1. For identical masses, momentum conservation requires the sum of the final velocities to equal the original moving object's velocity.
2. A full exchange of velocities, where the mover stops and the resting object takes on the original speed, satisfies that momentum equation.
3. Checking kinetic energy, the total kinetic energy before and after is identical, since it is the same single speed shared between the two situations.
4. Because both momentum and internal kinetic energy are conserved, this outcome describes an elastic collision, not an inelastic or impossible one.
_Source: OpenStax College Physics (CC BY 4.0), Ch 8 "Linear Momentum and Collisions", section 8.4 Elastic Collisions in One Dimension_
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