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A spy is standing on a bridge above a road. He notices a flatbed truck approaching at 30 m/s. He knows the telephone poles along the road are spaced 20 m apart. The bed of the truck is 20 m below the bridge. He needs to calculate how many poles away the truck should be when he jumps off the bridge so that he lands on the truck. How many poles away is the truck when he should jump? (Take g = 10 m/s²)
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Correct answer: 2
Solution
Time to fall 20 m: t = sqrt(2h/g) = sqrt(4) = 2 s. Truck travels 30*2 = 60 m in 2 s. Number of poles = 60/20 = 3. So the truck should be 3 poles away.
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