More conceptual MCQs :) Hi guys, After the concept test that I found quite difficult for some.. apologise for asking so many questions at a go. I try my best to solve for all just hope that any of you would be kind enough to correct any wrongs. I always have the urge to know the correct answers for those that I don't know! 1) For a cylinder to continue rolling on a frictionless surface, when viewed from its cross sectional area, which is true: a) Magnitude of CF at top, bottom, left and right the same. b) Magnitude of CF at top is greater than bottom. c) magnitude of CF at bottom is greatest. d)none of the above. My answer is (c) but I don't really know the explanation. I only recall that for example in vertical rotations, the bottom of the loop always requires a larger CF than the bottom as it needs to overcome the weight. Centripetal Force = CF 2) Bubbles in a boiling pot get larger as they rise to the surface. Which accounts for this? (i) Temp at surface higher than bottom of pot. (ii) External Pressure on bubbles less at the surface (iii) Additional water vapourise into the bubbles. I would say the first 2 is true, however for the (iii)? 3) 5J of heat flowed from a cooler region to a warmer region. Which of the statements are possibly or is/are true? (i) Work can be extracted during heat transfer and used to generate 5J of electrical energy. (ii) Work has been expended to transfer heat (iii) No work is extracted during heat transfer. My question is that how is it possible for heat to be extracted? 4) Which of the following does not involve diffraction? a) Hearing a person speak around a corner of a building even if he cannot be seen b) splitting of visible light into a colourful spectrum by a glass prism c) sea waves passing through a gap in the breakwaters. d) transmission of electrons through a thin film of diamond e) None of the above All seem to involve diffraction to me.. but seldom the answer is none of the above.. but in this case I think it is. 5) Which of the following is not an example of free oscillations? a) Swinging pendulum b) Ice cube bobbling up and down in water c) vibrations on a drum skin after it has been hit d) light rays in space travelling from sun to earth. e) tidal variations in sea level. I am stuck between b and e. In b there seem to be a driving freq - the water but it does not transfer energy to the cube right? for d I can't see how it is oscillating in the first place? 6) An ideal gas is confined in a container with flexible walls that always keep the pressure inside constant. Suppose the gas shrinks slowly to half its original volume. Which is definately false? a) Walls of container conduct heat and it is cooler outside b) walls of the container are semi-permeable and gas is diffusing out of container through walls. c) walls of container impermeable and av KE of gas molecules has fallen d) walls of container impermeable and made of perfect insulator to heat e) walls of container semi-permeable and conduct heat. I found this a tough one. As gas volume dcreases its temperature decreases at constant pressure. But I don't know how this links to the permeability of the walls? Thanks a lot guys... I assure you this is not homework it's a past test and I seek understanding rather than free answers from this wonderful forum. Thanks!