HCI 2014 P2

1 Name: __________________________________ ( ) Class: _____ HWA CHONG INSTITUTION END-OF-YEAR EXAMINATION 2014 PHYSICS Paper 2 Level: Secondary Three Duration: 1 hour 45 min Do not open this booklet until you are told to do so. INSTRUCTIONS TO CANDIDATES Write your name, index number and class on the top of this page. Answer the questions in Section A and B in the spaces provided. All workings must be shown. In Section B, for Question 10 answer ‘EITHER’ or ‘OR’. INFORMATION FOR CANDIDATES In Sections A and B the intended marks for each question or part of a question are given in brackets [ ]. Any working should be done in the space provided. When necessary, take g to be 10 ms-2 or 10 Nkg-1 ___________________________________________________________________ This question paper consists of 15 printed pages, including this page.

2 SECTION A (40 MARKS) Answer all the questions in this section 1. Pentaprism is used in a single -lens reflex camera to enable the user to see exactly what the lens of the camera views. Light entering the lens is reflected upward by a plane mirror to form an image on a piece of smoked glass. A fter two successive reflection inside t he pentaprism, light from the image emerges from the viewfinder and reaches the user's eye. (a) Explain why the plane mirror used in this system must be very thin. [2] ………………………………………………………………………………….. ………………………………………………………………………………….. ………………………………………………………………………………….. (b) Determine the maximum angle of incidence for refraction to occur when light passes from glass to air. Give that ηglass = 1.6 . [2] (c) Explain why light rays are reflected on the two sides of the pentaprism. [2] ………………………………………………………………………………….. ………………………………………………………………………………….. …………………………………………………………………………………..

3 2. William makes a glass of hot tea. After a while, he adds some ice cubes into the tea. William uses a temperature sensor to measu re the temperature of the tea. The figure below shows the temperature-time graph obtained. (a) Explain why the temperature of the tea increases from R to S. [2] ………………………………………………………………………………….. ………………………………………………………………………………….. ………………………………………………………………………………….. ………………………………………………………………………………….. (b) Estimate the temperature of the surroundings. [1] ………………………………………………………………………………….. (c) Another method to cool the hot tea without adding ice cubes is by leaving the cup of hot tea in the room to cool by evaporation. Explain how evaporation causes this cooling. [2] ………………………………………………………………………………….. ………………………………………………………………………………….. ………………………………………………………………………………….. …………………………………………………………………………………..

4 3. When a house is heated, thermal energy will be lost to the external surroundings. The figure below shows where the energy is lost from the house. (a) Explain how the thermal energy in the air within the home is lost through the roof to the surroundings. [2] ………………………………………………………………………………….. ………………………………………………………………………………….. (b) The table below gives cost-savings information about three methods of reducing energy loss. method of reducing energy loss installation cost saving on energy costs in one year number of years of saving needed to cover installation costs A Fitting carpets on the floor $600 $10 60 B Insulating the roof $300 $100 3 C Fitting modern windows $800 $20 40 i) Which method listed above is most efficient in saving cost? Explain your answer [2] ……………………………………………………………………………… ……………………………………………………………………………… ………………………………………………………………………………

5 ii) State one other way, not already mentioned, of reducing thermal energy loss from the house. [1] ……………………………………………………………………………… 4. A student conducted an experiment to determi ne the specific heat capacity of a liquid X. He immersed a heater in a beaker of liquid X at room temperature as shown below. The heater was switched on and a graph was obtained. (a) Another students feels that this method can be improved by first cooling liquid X to about 10 oC below room temperature and then heated to 10 oC above room temperature. Explain why this suggested method is more accurate. [2] ………………………………………………………………………………….. ………………………………………………………………………………….. ………………………………………………………………………………….. ………………………………………………………………………………….. (b) Another student insulated the set-up and obtained the graph shown below.

6 i) If the student has used a heater rated 180 W immersed in 0.60 kg of liquid X, calculate the heat capacity of liquid X. [2] ii) Give two reasons why the calculated value in b(i) must be larger than the actual value. [2] ……………………………………………………………………………… ……………………………………………………………………………… ……………………………………………………………………………… ……………………………………………………………………………… 5. In a laboratory experiment, B eaker A and Beaker B are filled with equal amounts of water. The temperature of the water in B eaker A and Beaker B are 60 C and 10 C respectively. A voltage reading of 3.6 mV is recorded when the two junctions of a thermocouple are placed separately in each beaker. If the water in Beaker B is now replaced by water at 100 C, determine the voltage reading of the thermocouple. [2] 3.6 mv Beaker A Beaker B 60C 10C

7 6. The figure below shows a boy on a sledge travelling down a slope. The boy and sledge have a total mass of 60 kg and are travelling at a constant speed. The angle of the slope to the horizontal is 35°. All the forces acting on the boy and sledge are shown in the figure below. (a) Determine the magnitude of W, the total weight of the boy and the sledge. [1] (b) By drawing a vector diagram, or otherwise , determine the magnitude of the resistive force R. [4] (c) Explain why the boy is travelling at a constant speed even though he is moving down a slope. [2] ………………………………………………………………………………….. ………………………………………………………………………………….. …………………………………………………………………………………..

8 7. In a sports game, one end of a long elastic string is tied to an athlete while the other end is fixed on a high platform as shown below. The athlete has to jump up into the air as high as he can. The elastic string prevents him from hitting the ground. An athlete of mass 70 kg is carried onto the platform of height 80 m by a lift in 20 s. The length of the unstretched elastic string is 40 m. (a) i) Find the potential energy gained by the athlete upon reaching the platform. [2] ii) Find the power required to lift the athlete to the platform. [2] (b) The athlete then jumps up into the air. He reaches a height of 81 m above the ground and then falls down again. If the average resistive force due to the elastic string on the ath lete is 2000 N, what is the lowest point above the ground he can reach? [3]

9 (c) In a real situation, is the lowest point reached by the man greater than, or equal to or smaller than the calculated value in (b) ? Explain. [2] ………………………………………………………………………………….. ………………………………………………………………………………….. ………………………………………………………………………………….. ………………………………………………………………………………….. SECTION B (30 Marks) Answer question Q8, Q9 and either Q10A or Q10B i