18   10 A student carried out an experiment to determine the viscosity of some honey. He filled a tall glass cylinder with honey as shown, and timed a ball bearing as it fell through the honey. cylinder rubber band honey ball bearing rubber band (a) The student placed rubber bands near the top and bottom of the cylinder. He started a stopwatch when the ball bearing passed the first band and stopped the stopwatch when the ball bearing passed the second band. He repeated this several times to determine a mean time. Criticise the student’s method. (2) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. (b) The time t for the sphere to fall through a distance of 25.0 cm is shown in the table. t / s 6.40 6.35 6.36 6.38 (i) Show that the mean velocity v of the ball bearing is about 0.04 m s−1. (3) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. Turn over 19   (ii) The student had three different types of honey available. Viscosity η is given by the following expression η = ( ) 2 B H 2 9 r g ρ ρ v − radius r of ball bearing = 5.50 × 10−3 m density of ball bearing ρB = 7750 kg m−3 density of honey ρH = 1360 kg m−3 Viscosity (at 20 °C) / Pa s Honey A Honey B Honey C 10.6 12.5 13.6 Deduce which honey the student used. (2) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. (Total for Question 10 = 7 marks)