A 13-foot ladder leans against a vertical wall. If the bottom slides away at 2 feet per second, how fast is the top sliding down when the bottom is 5 feet from the wall?
Answer and explanation
Correct answer: B. feet per second
- Step 1: Let . When , .
- Step 2: Differentiate with respect to time: .
- Step 3: Solve for : ft/sec.
Answer
feet per second.
Why not the others: inverts the ratio of vertical to horizontal positions; forgets to multiply by the horizontal velocity of 2 ft/sec; and miscalculates the vertical height as 15.
Practise more Differentiation.
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