5 3. A solid is formed by attaching two hemispheres to each end of a cylinder. If the total volume is to be 120 em , find the radius (in centimetres) of the cylinder that produces the minimum surface area. Express your answer correct to two decimal places. Mathematics 31 - Module 6 13 Assignment Booklet 4 4. The relation between distance s and velocity v is given by v = . Find the acceleration in terms of s. 3 5. A pebble is dropped into a still pond, causing ripples in the form of concentric circles. The radius r of the outer circle is increasing at a rate of 25 cm/s. When the radius is 100 cm, at what rate is the total area of the disturbed water increasing? Mathematics 31 - Module 6 14 Assignment Booklet 4 6. A construction worker pulls a 5 m plank up the side of a building under construction by means of a rope tied to the end of the plank. The opposite end of the plank is being dragged along the ground. If the worker is pulling at a rate of 15 cm/s, how fast is the end of the plank sliding along the ground when it is 2 m from the wall of the building? Express your answer correct to three 15 cm/s decimal places 5 1