12. Which of the following statements about a moving object is correct? A. When accelerating, the resultant force acting on it must be equal to zero. B. There must always be a non-zero resultant force acting on it. C. At a steady velocity, the resultant force acting on it must be equal to zero. D. Ata steady velocity, the air résistance must be equal to zero. 13. If the efficiency of a transformer is 100%, which of the following equations would be correct? A. N E = N E p p S S B. N I = N I S P P S C. NsIs = NpIp D. I E — I E P S S P 14. A freshly demagnetized bar magnet is placed in the East-West direction to ensure that A. the molecular Magnets remain randomly arranged. B. the molecular magnets are properly aligned. C. it is affected by the earth's magnetic field. D. the magnetic domains are within the earth's field. 15. Which of the following graphs of a charge Q against potential difference V across capacitor is correct? 16. A small amount of air is introduced into the vacuum above the mercury in a mercury barometer tube. The mercury level goes down because the air molecules A. heat the mercury and make it to expand. B. increase the pressure above the mercury. C. cool the mercury and make it to contract. D. decrease the pressure above the mercury. 17. Calculate the quantity of heat needed to change the temperature of 60 g of ice at 0 °C to 80 °C. [Specific latent heat of fusion of ice 5 -1 = 3.36 x l0 J kg 3 -1 -1 Specific heat capacity of water = 4.2x l0 J kg K A. 4.80 kJ B. 20.16 kJ C. 40.32 kJ D. 22.17 kJ 18. The wire of a platinum résistance thermometer has a résistance of 3.5 Ω at 0 °C and 10.5 Ω at 100 °C. Calculate the temperature of the wire when its résistance is 7.5 Ω. A. 78 °C B. 25 °C C. 36 °C D. 57°C 19. A transverse pulse of frequency 9 Hz travels 4.5 m in 0.6 s. Calculate the wavelength of the pulse. A. 3.33 m B. 0.30 m C. 0.83 m D. 1.20 m