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# KNEC KCSE Physics Paper 1 – 2015 – Machakos County Trial

## KNEC KCSE Physics Paper 1 – 2015 – Machakos County Trial

### SECTION A (25 Marks)

Answer ALL the questions in this section

1.

The figure below shows an empty beaker placed on the top of a pan calibrated in grammes. 50ml of
alcohol of density 0.8g/cm3 was added to the beaker.

Show on the diagram the new pointer position.

2 marks

2.

(a) What is surface tension? (1 Marks)
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(b) The figure below shows a funnel dipped into a liquid soap solution.

Explain what happens to the soap bubble when the soap is removed. (2 Marks)
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3 marks

3.

A boy on a bicycle accelerated uniformly at 1m/s2 for 10 seconds from an initial velocity of 4m/s.
Calculate the distance travelled in this time.
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3 marks

4.

An object is attached to a spring balance and its weight determined in air. It is then gently lowered into a
beaker containing water.
(i) State what happens to the reading. (1 Mark)
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(ii) Explain the force that causes observation in (i) above. (1 Mark)
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2 marks

5.

A metal cube weighs 1.0N in air and 0.8N when totally immersed in water.
Calculate
(i) Volume of water it displaces. (2 Marks)
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(ii) the density of the cube (2 Marks)
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4 marks

6.

State how the velocity of a moving fluid varies with pressure.
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1 marks

7.

The figure below shows a bottle opener.

A force of 30N is applied at a distance of 11cm from the pivot P. The force F on the bottle cap of 1.5cm from the pivot P. Calculate the force F on the edge of the cap.
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2 marks

8.

The figure shows a manometer used to measure the pressure difference between the air inside a plastic container and the atmosphere outside.

Calculate the force F exerted on the container.
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3 marks

9.

A student observes that in the morning an overhead electrical cable is straight and taut. At midday the student observes that the same cable has sagged. Explain these observations.
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2 marks

10.

A rubber tube is inflated to pressure of 2.7 x 105 pa and volume 3800cm3 at temperature of 25o C. It is then taken to another place where the temperature is 15C and the pressure is 2.5 x 105 pa. Determine the new volume
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3 marks

### SECTION B (55 Marks)

11.

(a) The figure below shows two containers filled with two different liquids to the same height.

It was found that the pressure at the bottom of A is greater than that at B. Explain (1 Mark)
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(b) The figure below shows a car braking system. The brake fluid is an oily liquid.

The brake drum rotates with the wheel of the car.
(i) Explain how pushing the brake pedal makes the brake rub against the drum. (4 Marks)
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(ii) The cross-sectional area of the master piston is 2.0cm2. A force of 140N is applied to the master
piston.

(I) Calculate the pressure created in the brake fluid by the master piston. (2 Marks)
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(II) The cross-sectional area of each slave piston is 2.8cm2. Calculate the force exerted on each slave
piston by the brake fluid.
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(III) The force exerted on the master piston is greater than the force applied by the foot on the brake
pedal. Using the principle of moments, explain this (2 Marks)
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(c) The figure below shows a master cylinder sealed at one end. Instead of brake fluid, the cylinder
contains air.

When a force is applied to the piston, the length d changes from 6.0cm to 4.0cm. The pressure of the
air increases but the temperature stays constant.
(i) Describe how the molecules of air exert a pressure. (1 Mark)
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(ii) Explain why the pressure increases even though the temperature stays constant. (1 Mark)
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(iii) The initial pressure of the air inside the cylinder is 1.0 x 105 pa. Calculate the final pressure of the
air. (2 Marks)
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15 marks

12.

(a) What is a machine? (1 Mark)
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(b) Two gear wheel have a 80 teeth (driven) and 20 teeth (driving) and lock with each other. They are
fastened on axles of equal diameters such that a weight of 150N attached to a string round one axle
will just raise 450N on the other axle.
Calculate
(i) M.A (2 Marks)
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(ii) V.R (2 Marks)
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(iii) Efficiency of the machine. (2 Marks)
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(c) The graph below shows the variation of force with distance for a body being towed.

Calculate the total work done on the body. (3 Marks)
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10 marks

13.

(a) Distinguish between distance and displacement. (2 Marks)
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(b) A jet fighter moving horizontally at a speed of 200m/s at a height of 2km above the ground is to drop a bomb to hit a target on the ground. How long does the bomb stay in air after release before it hit the target? (3 marks)
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(c) Two equal masses travel towards each other on a frictionless air track at speeds of 60cm/s and
40cm /s. They stick together on impact.

What is the velocity of the masses after impact?
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(d) The figure shows a simple pendulum oscillating between Y and Z.

State the type of energy the body passes at
(i) Position y (1 Mark)
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(ii) Position x (1 Mark)
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10 marks

14.

(a) (i) Define the term latent heat of fusion. (1 Mark)
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(b) In an experiment to determine the power of an electric heater, melting ice was placed in a container with an outlet and the heater placed in the ice as shown below. The melted ice was collected.

(i) Other than the current and voltage, state the measurement that would be taken to determine the
quantity of heat absorbed by the melted ice in unit time. (1 Mark)
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(ii) If the latent heat of fusion of ice is L, show how measurement in (i) above would be used in
determining the power P of the heater. (2 Marks)
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(iii) It is found that the power determined in this experiment is lower than the manufacturer’s value
indicated on the heater. Explain. (1 Mark)
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(c) A mass of wax of 1kg was heated uniformly by a 100W heating element until it melted. The graph
below shows how the temperature of the wax varies with time.

(i) Explain what is happening in the region.
AB
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BC
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(ii) Calculate the specific heat capacity of the wax. (2 Marks)
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(iii) Calculate the specific latent heat of fusion of wax. (2 Marks)
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15 marks

15.

(a) A stone of mass 450g is rotated in a vertical circle at 3 revolutions per second. If the string has a
length of 1.5m, determine:

(i) the linear velocity (3 Marks)
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(ii) The tension of the string at positions A and B. (4 Marks)
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(b) State two factors affecting centripetal force. (2 Marks)
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9 marks