The kinetic energy, K, of an object varies jointly with the mass of the object and the square of the velocity of the object. A 50-kg object moving at a velocity of 20 meters per second has 10,000 joules of kinetic energy. How many joules of kinetic energy does a 25-kg object moving at a velocity of 10 meters per second have?

Since kinetic energy varies jointly with mass and the square of velocity, K = c mv². The given object has 50 × 20² = 20,000 in mass-velocity units, so the energy is half that amount; thus c = 0.5. For the new object, K = 0.5 × 25 × 10² = 1,250 joules, which is choice B, 1,250 joules.

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