An engine alone runs at 42 km/h. Its speed drops by an amount proportional to the square root of the number of wagons attached; with 9 wagons it runs at 36 km/h. What is the greatest number of wagons it can pull and still move?

Question

Accepted Answer

440. Drop =k√n: 6=k×3 → k=2. Speed zero when 2√n=42 → n=441. At 441 it stops, so at most 440 wagons.

An engine alone runs at 42 km/h. Its speed drops by an amount proportional to the square root of the number of wagons attached; with 9 wagons it runs at 36 km/h. What is the greatest number of wagons it can pull and still move?

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