## PHYSICS PAPER 1 - 2020 KCSE PREDICTION SET 1 (QUESTIONS AND ANSWERS)

Instructions to candidates:

• This paper consists two sections A and B
• Answer all questions in Section A and B in the spaces provided.
• All working MUST be clearly shown.
• Mathematical tables and electronic calculators may be used.
• Candidates should answer the questions in English

SECTION A (25 MARKS)
Answer ALL questions in this section in the spaces provided

1. The figure 1, shows a micrometer screw gauge that has a zero error of +0.02. State the actual reading of the micrometer screw gauge. (1mk) 1. In the figure 2, the U-tube contains two immiscible liquids P and Q. If the density of Q is 900kg/m3 and that of P is 1200kg/m3, calculate the height of liquid Q. (3mks) 1. A force of 10N towards the right hand side and 6N towards the left hand side acts upon a body. What is the resultant force? (2mks)
1. A trolley of mass 1.5kg moving with a velocity of 1.2 ms-1 collides inelastically with a second trolley of mass 0.5kg moving in the opposite direction with a velocity of 0.2ms-1.
1. What is an inelastic collision?                                                 (1mk)
2. Determine the velocity of the trolleys after collision.          (2mks)
1.
1. What is surface tension?                                                 (1mark)
2. Figure 3, shows a funnel dipped into a liquid soap solution. Fig. 3
Explain what happens to the soap bubble when the funnel is removed.             (1mark)
1. Figure 4, shows a clinical thermometer which is not graduated. Fig. 4

1. Name the parts indicated with letters: A and B (1 mark)
2. Mark the appropriate scale range in degrees Celsius (1 mark)
1. Figure 5, shows air flowing through a pipe of non-uniform cross-sectional area. Two pipes A and B are dipped into liquids as shown. .
Fig. 5
1. Indicate the levels of the liquids in Pipe A and pipe B. (1 mark)
1. The figure 6, shows a flask fitted with a glass tube dipped into a beaker containing water at room temperature. The cork fixing the glass tube is tight. Fig. 6
State with reason what would be observed if cold water is poured on to the flask. (2marks)
1. The figure 7, shows three identical springs which obey Hooke’s law. Fig. 7
Determine the length Xcm.                                            (3 marks)
1. Using the idea of particles, explain why the pressure inside the tyre is increased when it is pumped up       (2marks)
1. Give one fact which shows that heat from the sun does not reach the earth surface by convection.                        (2marks)
2.
1. Give a reason why water is not suitable as a barometric liquid. (1 mark)
2. Explain why a lift pump is unable to raise water from a borehole where the level ofwater is 20m below the ground level.                                                                     (1 mark)

SECTION B (55 Marks)
Answer ALL questions in this section in the spaces provided.

1.
1. A force of 7.5N stretches a certain spring by 5 cm. Calculate the work done in stretching this spring by 8.0 cm.                                                           (3 marks)
2. Figure 8, shows a cross-section of a handle of a screw jack 70 cm long. The pitch of the screw is 0.8 cm Fig. 8
Given that the efficiency is 65%, calculate:
1. the velocity ratio of the system    (2 marks)
2. the mechanical advantage of the screw jack.                                             (2 marks)
3. Sketch a graph of efficiency against Load (1 mark)
4. Draw a single moving pulley with a velocity ratio of 2. (2 marks)
1.
1. State Hooke’s law                                     (1mark)
2. The graph provided is of force (y-axis) against extension. 1. From the graph determine the work done in stretching spring by 3cm (3marks)
2. Use the graph to determine the spring constant. Give your answer in SI units    (3marks)
3. State three factors that affect the spring constant                                   (3marks)
1.
1. Define latent heat of vaporization. (1 mark)
2. Figure 9, shows a set up by a student to determine the specific latent heat ofvaporization of a liquid. Fig. 9
1. Identify the parts labelled X and Y (2 marks)
2. State the measurements that should be taken. (2 marks)
3. Describe how the set up can be used to determine the specific latent heat of vaporisation of the liquid.               (5 marks)
4. What is the purpose of the condenser? (1 mark)
2.
1.
1. State Archimedes’s Principle. (1 mark)
2. An object weighs 1.04N in air, 0.64N when fully immersed in water and 0.72N when fully immersed in a liquid. If the density of water is 1000 kg m-3, find the density of the liquid.(4 marks)
2.
1. State the law of floatation (1 mark)
2. Give a reason why a steel rod sinks in water while a ship made of steel floats on water. (1 mark)
3. Draw a clearly labelled diagram of a common hydrometer, which is suitable for
Measuring the densities of liquids varying between 1.0 and 1.2 g cm-3.(2 marks)
3. Figure 10, shows a buoy, B, of volume 40 litres and mass 10 kg. It is held in position in sea water of density 1.04 g cm-3 by a light cable fixed to the bottom so that of the volume of the buoy is below the surface of the sea water. Determine the tension T in the cable. (4 marks) Fig. 10
3.
1. State Pressure Law (1 mark)
2. State one basic assumption of the kinetic theory of gases. (1marks)
3. Figure 11, shows a set up that may be used to verify Pressure law. Fig. 11
1. State the measurements that may be taken in the experiment. (2 marks)
2. Explain how the measurement in (i) above may be used to verify Pressure law.         (4 marks)
4. A bicycle tyre is pumped to a pressure of 2.2 x 105 pa at 23o After a race the pressure is found to be 2.6x10pa. Assuming the volume of the tyre did not change, what is the temperature of the air in the tyre.                                                                  (3 marks)

## MARKING SCHEME

1. Actual reading = (6.20 – 0.02) mm =    6.18mm √1
1. h, ℓ, g = h2p2g √1
h x 900 = 0.06 x 1200 √1
h = 0.08m = 8cm  √1
1. 4N √1
Resultant force √1 = (10 – 6)N = 4N √1 towards the √1 right hand side.
2.
1. A collision in which objects combine / fuse, losing kinetic energy in the process.
2. Final momentum = Initial momentum (0.5 + 1.5) V = (1.5 x 1.2) + (0.5 x 0.2)
2.0V = 1.8 + 0.1
2.0V = 0.9
V = 0.95 m/s
3.
1. Surface tension is the force per unit length acting on the surface of a liquid and perpendicular to one side of an imaginary line drawn in the surface.
→Surface tension is the tangential force acting at right angles in the surface of a liquid per unit length across any line in the surface
→ (It is the property that makes a free liquid surface act like a stretched elastic skin).
2. Bubble flattens to a film and moves up the funnel in order to make its surface area be as small as possible due to surface tension
4.
1. A – Bulb           B – Constriction √1
2. 5.
1. 2. The liquid level is high in pipe B than in pipe A because the pressure is low due to the high speed of the air.
1. Water is sucked in to the glass tube
Air in the flask contracts when cooled. Lowering pressure inside                 (2 marks)
2. (3mks)
1. More air is pumped into the tyre. The number of particles colliding with the walls increases. the increase in the rate of change of momentum, hence the force per unit area increase. √
1. Convection takes place in air upwards direct due to density effect √1
Convection requires material medium but the space between the sun and the atmosphere has no material medium.
1.
1. It has low densityü hence along column of water is supported by atmospheric pressure.
2. The maximum height the can be raised is 10m since the pumpü operates due to atmospheric pressure.
1.
1. m1u1 + m2u2 = m1v1 + m2v2
4 kg x 0 m/s + 0.012kg x 0 = 0.012 kg x 700 m/s – 4 kg x v2
0 = 8.4 kg m/s - 4 kg v2
v2 = 8.4 kg m/s = 2.1 m/s
4 kg
2.
1. V.R. = Effort Distance  = 2π x 70 cm   = 2 x 3.14 x 70     V.R. = 549.50
2. M.A. = Efficiency x V.R.;     M.A. = 0.65 x 549.50
M.A. = 357.12
3. Graph of efficiency against load 4. simple moving pulley with velocity ratio 2. 1. For an elastic material, extension is directly proportional to the force producing it provided the elastic limit is not exceeded.                                                           (1mk)
2. The graph provided is of force (y-axis) against extension
1. From the graph determine the work done in stretching spring by 3cm
= Fe   = W­ = ½Fe
=   ½ x 3 x 0.03
= 0.045J
2. use the graph to determine the spring constant
(4 − 1) x 10-2
3
3x 10-2
= 100 N/m
3. State three factors that affects the spring constant
Diameter of the spring
Number of turn per unit length
The material of the spring.
1.
1. Archimedes’ Principle states that when a body is partially or wholly immersed in a fluid, it experiences an upthrust equal to the weight of the fluid displaced.
2. Upthrust in liquid = 1.04 – 0.72 = 0.32N
Upthrust in water = 1.04 – 0.64 = 0.40
Density of liquid = Density of liquid = 2.
1. A floating body displaces its own weight of the fluid its floats.
2. A ship is hollow and displaces a large volume of water to provide enough upthrust equal to its own weight, while steel rod sinks since it is denser than water.
3. Hydrometer 4. Volume of water displaced = ¾ x 40 = 30 l = 0.03 m3
Weight of buoy = mg = 10 x 10 = 100N
Weight of sea water displaced = density x gravity x volume
= 1.04 x 103 x 10 x 0.03 N = 312N
Weight of sea water displaced = Upthrust
Tension T = Upthrust – Weight of buoy = 312 – 100; T = 212N
1. Pressure law states that the pressure of a fixed mass of gas is directly proportional to its absolute temperature, provided the volume is kept constant.
2. That gas consists of very small particles known as molecules
3.
1. Measurements: temperature with thermometer and pressure with bourdon gauge
Heat the water as you stir gently
Tabulate various values of temperature T and corresponding values of Pressure P
2. Plot a graph of Pressure (P) against absolute temperature (T)
The graph is a straight line (determine the value of )
4. 