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A block slides on a frictionless surface at 40 m/s and then breaks into two equal-mass pieces. One piece continues forward at 60 m/s along the original direction. The fractional change in the total kinetic energy can be written as x: 4. Find x.

1. 1
2. 2
3. 3
4. 4

Correct answer: 1

Solution

Momentum conservation gives the second piece a speed of 20 m/s. The kinetic energy increases, and the fractional change works out to 1/4, i.e. 1: 4.

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