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A 2 m man walks at 5 km/h away from a 6 m lamp post. How fast does his shadow's tip move?
A5.0 km/h
B7.5 km/h
C12.5 km/h
D10.0 km/h
Answer & Solution
Correct answer: B. 7.5 km/h
Similar triangles give the tip distance y = 1.5x, so dy/dt = 1.5 × 5 = 7.5 km/h.
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