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1.7 Differentiation

1.7 Differentiation

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Question 255
i.

A spherical drop of industrial lubricant is being injected into a precision-engineered cavity. The volume, VVV, of the drop is increasing at a constant rate of 180π mm3 s−1180\pi \text{ mm}^3\text{ s}^{-1}180π mm3 s−1. Calculate the rate of increase of the radius, rrr, of the drop in mm s−1 \text{mm s}^{-1}mm s−1 at the moment when the radius is exactly 3 mm3 \text{ mm}3 mm. [The volume VVV of a sphere of radius rrr is given by V=43πr3V = \frac{4}{3}\pi r^3V=34​πr3]

[5]
ii.

The depth of sediment, y metresy \text{ metres}y metres, settling at the bottom of an industrial filtration tank is monitored. The rate of change of the depth of the sediment is modeled by the differential equation

dydt=ky2 \frac{\text{d}y}{\text{d}t} = \frac{k}{y^2} dtdy​=y2k​

where kkk is a positive constant and ttt hours is the time after monitoring began. Given that:

  • at the start of monitoring (t=0t = 0t=0), the sediment depth was 2 metres2 \text{ metres}2 metres.
  • after 555 hours of monitoring, the sediment depth had reached 4 metres4 \text{ metres}4 metres.
  • after TTT hours of monitoring, the sediment depth reached 6 metres6 \text{ metres}6 metres.

Solve the differential equation to determine the value of TTT. Give your answer to one decimal place.

[8]
Markscheme

1.7 Differentiation Questions

  1. A Level
  2. /Maths
  3. /1.7 Differentiation

425 exam-style questions on OCR A Level Maths 1.7 Differentiation, covering 1.7.1 Derivative as gradient of the tangent, 1.7.2 Gradient of the tangent at a point, 1.7.3 Sketching the gradient function, 1.7.4 Second derivatives, 1.7.5 Second derivative as rate of change of gradient, 1.7.6 Convex, concave and points of inflection (A-level only), 1.7.7 Differentiation from first principles for powers of x, 1.7.8 Differentiation from first principles for sin x and cos x (A-level only), 1.7.9 Differentiating x^n, 1.7.10 Differentiating e^(kx) and a^(kx) (A-level only), 1.7.11 Differentiating trigonometric functions (A-level only), 1.7.12 Derivative of ln x (A-level only), 1.7.13 Tangents and normals, 1.7.14 Stationary points, 1.7.15 Increasing and decreasing functions, 1.7.16 Points of inflection (A-level only), 1.7.17 Product and quotient rules (A-level only), 1.7.18 Chain rule (A-level only), 1.7.19 Parametric and implicit differentiation (A-level only), 1.7.20 Constructing differential equations (A-level only), and 1.7 Differentiation. Each one has a worked solution and a mark scheme showing where the marks go.

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