Differentiation - Problems Involving Maximisation and Minimisation

Differentiation - Problems Involving Maximisation and Minimisation

TGM Original Questions

As shown in the diagram, a person in a boat is \(3\) km from the nearest point from the straight beach. The person is to get to a cabin \(6\) km along the beach. It is known that the boat travels at \(4\) km/h and the person walks at \(5\) km/h. Assume that the person lands at a point \(x\) km from the point directly opposite to the original position.

  1. Find, in terms of \(x\), the total time (in hours) taken for the person to reach the cabin.
  2. Find the value of \(x\) for which the total time taken is the minimum and find this minimum time.

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Answer:(i) \(T=\dfrac{\sqrt{x^2+9}}{4}+\dfrac{6-x}{5}\text{ h}\) (ii) \(x=4\text{ km}\), minimum time \(=\dfrac{33}{20}\text{ h}=1.65\text{ h}\)

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