Engineering Board Exam Reviewer · Related Rates (Time Rates) · medium
A ladder 10 ft long leans against a vertical wall. If the bottom slides away from the wall at 2 ft/s, how fast is the top sliding down the wall when the bottom is 6 ft from the wall?
- 1.5 ft/s
- 2.0 ft/s
- 0.75 ft/s
- 1.2 ft/s
Answer
A. 1.5 ft/s
Solution
x2+y2=100. At x=6, y=8. Differentiating: 2xdx/dt+2ydy/dt=0 dy/dt=-x/ydx/dt=-6(2)/8=-1.5 ft/s.
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