`NAME………………………………………………..ADM NO………………..CLASS……….

KCSE ONLINE EXAMSTERM 2 END TERM EXAM 2014

PHYSICS FORM 3

INSTRUCTIONSAnswer all the questions in the spaces providedAll working must be clearly shown.Take acceleration due to gravity g=10m/s2, Density of water = 1000kg/m3

SECTION A (35MKS)

1. What is the reading on the micrometer screw gauge shown below? (2mks)

2. It is safe to hold the other end of a burning match stick. Explain why. (1mk)

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3. A machine of efficiency 80% is used to lift a load of 480N with an effort of 60N. Calculate the velocity ratio of the machine. (2mks)

In the circuit shown, the emf of the cell is 6v and its internal resistance is 0.4. Calculate;

a) Effective resistance in the circuit. (2mks)

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b) The current through the 12 resistance. (2mks)

4. State the basic law of electrostatics. (1mk)

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5. A person of mass 70kg stands on a scale balance in a lift at a particular instance when the lift is accelerating upwards at 2m/s2. Calculate the reading on the scale in Newtons at the instance. (2mks)

6. An object is placed 15cm in front of a concave mirror. Determine the distance between the object and the real image if the magnification of the mirror is 4. (2mks)

7. The power of an engine s 20kw. What is the maximum amount f work the engine can do in 6 seconds? (2mks)

8. Calculate the maximum pressure that a glass block of density 2.5g/cm3 would exert on a horizontal surface if the block measures 20cm by 10cm by 5cm. (3mks)

9. State the principle of levers. (1mk)

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10. In the figure below indicate the levels (height) of water in tubes B and C. (2mks)

11. An object is projected vertically upwards with a velocity of 25m/s.a) What will be the maximum height reached. (2mks)

b) How long will it take to return to the same level of projection? (2mks)

12. What property of light leads to the formation of shadows? (1mks)

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a) A uniform 1 meter plunk is balance horizontally by the shown forces. Calculate force F1. (3mks)

b) What is the mass of the 1 meter plunk? (1mk)

13. State one way of changing the size of the image formed by a pin-hole camera. (1mk)

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14. A body has 20J of kinetic energy. What would be its kinetic energy if its velocity is doubled? (3mks)

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SECTION B (65 MARKS)

15. a) A pinhole camera is used to take a photograph of a tree which is 8.0 away from the pinhole. If the length of the box used is 20cm and the height of the image of the tree on the screen is 12cm, calculate;

i) The magnification produced by the pinhole camera. (2mks)

ii) The height of the tree. (2mks)

b) Draw a ray diagram to show how a concave mirror produces an upright virtual image of an object.(3mks)

16. Using a diagram of plane water waves, explain what happens to wavelength when it moves from the deep part to the shallow part. (2mks)

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17. The figure below shows on electromagnet that was used to attract a metal ball.

a) Suggest with a reason a suitable metal for the cone. (2mks)

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b) Indicate on the diagram the polarity of the electromagnet when the switch S is closed. (1mk)

c) Suggest two changes that might be made to the apparatus which would enable a heavier ball to be attracted by the electromagnet. (2mks)

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d) How would the operation of the electromagnet be affected, if the polarities of the battery are reversed. (2mks)

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e) Briefly describe how you would demagnetize a magnet using electrical method. (3mks)

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18. The figure below shows how a student set up a circuit using 3 identical bulbs X, Y and Z each rated at “12V, 2.0A”.

i) When operating normally, calculate the resistance of one of the bulbs. (1mk)

ii) Calculate the effective resistance of the three bulbs connected in the figure. (2mks)

iii) Calculate the current drawn from the power supply. (1mk)

iv) Draw a circuit diagram showing the three bulbs X, Y, and Z connected in such a way that they would all work at same brightness. (2mks)

v) What would be their effective resistance in the new circuit. (2mks)

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vi) Calculate the current drawn in the new circuit. (1mk)

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19. a) Calculate the tension developed in a string supporting a mass of 120g. (1mk)

b) Explain why when a horse running fast suddenly stops, the rider is thrown forward over the horse’s head. (1mk)

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c) A train of mass 3 x 104kg moving with a velocity of 72 km/h is brought to rest in 30s. Calculate.

i) The stopping distance due to the braking force. (3mks)

ii) The breaking force. (2mks)

d) A gun of mass 9 x 103g fires a bullet of 50g at a velocity of 250m/s. Find the recoil velocity of the gun. (3mks)

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e) A body of mass 300kg moving with a uniform velocity of 30m/s collided with another body at rest. The two then begin to move together with a uniform velocity of 20m/s.

i) Which type of collision is this? (1mk)

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ii) Calculate the mass of the second body. (2mks)

20. a) Name the transducers in the following energy conversions.

Energy Conversions Transducersi Chemical to electrical

ii Sound to electrical

iii Mechanical to electrical

b) A worker wants to load a drum of weight 1000N on a truck whose floor is 1m above the ground. The man rolls the drum up a plant 3m long with a force of 400N. Calculate;

i) The work output. (2mks)

ii) The work input. (2mks)

iii) The efficiency of the machine. (2mks)

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c) While a screw jack an effort of 10N has t be applied to lift a load of 8000N. The length of the handle is 35cm and the pitch of the screw is 0.25cm. Calculate;

i) Mechanical advantage. (1mk)

ii) Velocity ratio of the machine. (2mks)

21. The data below represents the motion of a car over a period of 7 seconds.

Time (s) 0 1 2 3 4 5 6 7Displacement (m) 0 15 30 45 60 74 80 83

a) Plot a graph of displacement against time on the graph paper provided. (5mks)

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b) Describe the motion of the car in the first 4 seconds. (2mks)

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c) Determine the velocity of the car when t=4.5 seconds. (2mks)

d) Determine the velocity of the car when t=5.5 seconds. (2mks)

e) What is the acceleration of the car between t=4.5 seconds and t=5.5 seconds. (1mk)

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