The power consumption, www (in watts), of a submersible exploration drone at depth ddd (in meters) is modelled by the equation
w=3d3−40d+kd,d>0 w = 3d^3 - 40d + \frac{k}{d}, \quad d > 0 w=3d3−40d+dk,d>0where kkk is a constant. The drone has a stationary point in its power consumption at depth PPP where d=2d = 2d=2.
Show that k=−16k = -16k=−16.
Determine the nature of the stationary point at PPP, justifying your answer.
The power consumption model suggests there is a second stationary point at a different depth.
Using algebra, find the depth of this second stationary point.
717 exam-style questions on Edexcel A Level Maths Differentiation, covering 9.1 Differentiating sin x and cos x, 9.2 Differentiating exponentials and logarithms, 9.3 The Chain Rule, 9.4 The Product Rule, 9.5 The Quotient Rule, 9.6 Differentiating Trigonometric Functions, 9.7 Parametric Differentiation, 9.8 Implicit Differentiation, 9.9 Using Second Derivatives, and 9.10 Rates of Change. Each one has a worked solution and a mark scheme showing where the marks go.