# PHYSICS PAPER 1 - KCSE 2019 MOKASA PRE MOCK EXAMINATION

SECTION A (25 MARKS)
Attempt all the questions in the spaces provided.

1. Define a free fall.                                                                                           (1 mark)
1. The figure 1 below shows a force of 40N acting on a body of mass 4kg. The coefficient of friction between the surfaces is 0.05.

Determine the acceleration of the body.          (3 marks)
1. A uniform bar is pivoted at a point 30cm from one end.  A force of 12N at the end of the shorter side keeps the bar in equilibrium.  If the length of the bar is 1 metre, determine the weight w, of the bar.                       (2 marks)
1. A student observed some pollen grains on the surface of water in a beaker with the help of hand lens as shown figure below.

1. State the observation made.                                                            (1 mark)
2. Explain the observation in (a) above.                                              (1 mark)
3. What conclusion can be drawn from the above experiment?     (1 mark)
1. An immersion heater consumes a voltage of 240V and a current of 10A.  If it is used to heat 5kg of water at 200C, find the final temperature of water after 7 minutes. (Take the specific heat capacity of water = 4200 J/kgk)       (3 marks)
2. The figure 3 below shows a rubber bladder filled with air and fixed at the bottom of a water container and held with a cotton string.

State and explain the observation made when water is heated gently for a few minutes.                      (2 marks)
3. The figure 4 below shows a pipe of varying cross-section.  Three vertical tubes X, Y and Z of same diameter are fixed to the section A, B and C of the pipe respectively as shown below.

Given that the water flows in the direction shown by the arrow, indicate on the diagram the relative levels of water in Y and Z.                                                 (1 mark)
1. A smooth wooden plane is inclined at an angle of 300 to the horizontal as shown in Figure 5 below.  An object of mass 10kg is pulled steadily up the plane by a force of 60N.

Determine;
1. the velocity ratio of the inclined plane.                                          (2 marks)
2. efficiency of the system.                                                                   (2 marks)
1. The Figure 6 below shows a spiral spring when not compressed and when compressed by a mass of 4.0kg.

1. uncompressed spring
2. Compressed spring
Determine the elastic potential energy stored by the compressed spring in (b).        (3 marks)
1. The bicycle pump shown in Figure 7 below is one of the applications of pressure in gases.

Explain how the leather washer functions during;                                   (2 marks)
1. backstroke
2. forward stroke
1. Explain how greenhouse effect increases the average temperate of the earth. (2 marks

SECTION B (55 MARKS)

1.
1. The Figure 8 below shows a planet Venus orbiting the sun in a circular orbit at constant speed.

1. State what provides the centripetal force.                         (1 mark)
2. Indicate the direction of centripetal force on the planet.            (1 mark)
2. A stone is thrown with a horizontal velocity u from the top of a building of height 125m so as to hit a target on the ground 75m from the base of the building as shown in Figure 9 below.

Calculate:
1. the time taken for the stone to hit the target.                    (2 marks)
2. the horizontal velocity, u, of the stone.                              (2 marks)
3. A stone of mass 0.5kg is attached to a string of length 0.5m which will break if the tension exceeds 20N.  The stone is whirled in a vertical plane, the axis of rotation being above the ground, as shown in the Figure 10 below.
4. The angular velocity is gradually increased until the string breaks.
1. In what position is the string most likely to break?                      (1 mark)
2. At what angular velocity, w, will the string break?                        (3 marks)
1.
1. Define the term atmospheric pressure.                                         (1 marks)
2. The Figure 11 below shows a hydraulic lift supporting a load of 150kg.  Its cross-sectional areas A1 and A2are 0.02m2 and 0.4m2 respectively.

The length of the effort arm is 1m and the length of the plunger from the pivot is 0.4m.
Determine:
1. the pressure exerted by 150kg mass.                                (1 mark)
2. the pressure exerted by F1 on the smaller piston.                        (1 mark)
3. the force F1.                                                                           (2 marks)
4. the applied force, Fe.                                                                        (2 marks)
5. the mechanical advantage.                                                   (2 marks)
6. the velocity ratio of the system.                                          (2 marks)
7. the efficiency of the system.                                                 (2 marks)
2. An unknown amount of kerosene was heated using a heater rated 240V, 100W.   The temperature of kerosene was recorded at 2 minutes intervals. The graph OMN in the Figure 12 below was plotted.
1.
1. State the boiling point of kerosene.                                                            (1 mark)
2. What happens to the heat supplied by the heater on part MN of the graph?    (1 mark)
3. From the graph determine the electrical energy supplied by the heater on part OM of the graph.                                           (2 marks)
4. Determine the mass of kerosene that was used in the experiment.
(Assume heat gained by the beaker and the surrounding is negligible)              (3 marks)
Take specific heat capacity of kerosene to be 2200 JKg-1K-1 .
2. The Figure 13 below shows a velocity-time graph for a steel ball falling through a viscous fluid.

Explain the nature of the curve in;
1. section PQ. (1 mark)
2. section QR. (1 mark)
3. If the graph shown above is of a ball falling through water, sketch on the same axis a graph for the ball falling through glycerine. (1 mark)
3.
1. A student constructed the simple thermometer shown in the figure 14 below.
1. Why must the tube be made of thin glass?                        (1 mark)
2. Assuming that the weight of the pellet is negligible, what will the pressure of the trapped air be when the tube is vertical?  Explain.  (2 marks)
2. She placed the thermometer in water which was at various temperatures and obtained the graph shown in Figure 15 below.

1. Use the graph to find the temperature when the air column is zero. (1 mark)
2. What is the temperature called?                                         (1 mark)
3. Which of the gas laws does this set-up apply?  Verify.     (1 mark)
3.
1. State the SI unit of momentum as used in Physics.           (1 mark)
2. A bullet of mass 2g is fired horizontally into a block of wood of mass 498g. The block is suspended by a light inextensible string so that it is able to move in a verticalplane.  The block and the bullet move together through a vertical distance of 8.6cm as shown in figure 16 below.
3. Calculate the change in gravitational potential energy of the block and bullet.                                                            (2 marks)
4. Calculate the initial velocity of the block and bullet after they start moving together.                                             (2 marks)
5. Determine the speed of the bullet before the impact with the block.                                                                             (2 marks)
1.
1. State the law of floatation.                                                               (1 mark)
2. The densities of liquids may be measured using hydrometers.  The hydrometer in the Figure 17 consists of a weighted bulb with a thin stem , and is floating to the depth shown when it is immersed in a liquid whose density is 0.8g/cm3. The hydrometer is then floated in two liquids whose densities are 1.0g/cm3 and 1.25g/cm3.

1. On the diagram, mark with letters M and N the positions on the scale of the 1.25 g/cm3 and 1.0g/cm3 (1 mark)
2. The hydrometer has a mass of 165g and the stem has a uniform cross-sectional area of 0.75 cm2.  Calculate;
1. the change in the submerged volume of the hydrometer when it is first placed in a liquid of density 1.00 g/cm3 and then in the liquid of density 1.25 g/cm3.  (3 marks)
2. the distance on the stem between the 1.0 g/cm3 and 1.25 g/cm3 graduations.                                           (2 marks)
3. State two ways of improving the sensitivity of the above hydrometer. (2 marks)

## MARKING SCHEME

1. Define a free fall.                                                                                           (1 mark)
A body falling under the influence of gravity (alone).
1. The figure below shows a force of 40N acting on a body of mass 4kg. The coefficient of friction between the surfaces is 0.05.

Determine the acceleration of the body.                                                      (3 marks)

1. A uniform bar is pointed at a point 30cm from one end.  A force of 12N at the shorter end keeps the bar in equilibrium.  If the length of the bar is 1 metre, determine the weight w, of the bar.                                                                                       (2 marks)

1. A student observed some pollen grains on the surface of water in a beaker with the help of hand lens as shown below.

1. State the observation made.                                                            (1 mark)
Pollen grains were seen to be moving in constant random motion.
2. Explain the observation in (a) above.                                             (1 mark)
The grains were being hit continuously by the invisible water molecules which were also in random motion.
3. What conclusion can be drawn from the above experiment.      (1 mark)
Matter is particulate.
1. An immersion heater consumes a voltage of 240V and a current of 10A.  If it is used to heat 5kg of water at 200C, find the final temperature of water after 7 minutes. (Take the specific heat capacity of water = 4200 J/kgk)       (3 marks)
Heat supplied by heater = Heat gained by water.

2. The figure below shows a rubber bladder filled with air and fixed at the bottom of a water container and held with a cotton string.

State and explain the observation made when water is heated gently for a few minutes.                                                                                                      (2 marks)
Tension reduces. When water is heated it expands and its density decreases.  This results into upthrust decreasing.
U↓= Vs ρ(L↓)g
Since U =  u = Tφw, then tension must also reduce since weight is constant.
3. The figure below shows a pipe of varying cross-section.  Three vertical tubes X, Y and Z of same diameter are fixed to the section A, B and C of the pipe respectively as shown below.

Given that the water flows in the direction shown by the arrow, indicate on the diagram the relative levels of water in Y and Z.                                        (2 marks)
1. A smooth wooden plane is inclined at an angle of 300 to the horizontal as shown below.

An object of mass 10kg is pulled up the plane by a force of 60N.  Determine;
1. the velocity ratio of the inclined plane.                                          (2 marks)

2. efficiency of the system.                                                                   (2 marks)

1. The diagram below shows a spiral spring when not compressed and when compressed by a mass of 4.0kg.

1. uncompressed spring
2. Compressed spring
Determine the elastic potential energy stored by the compressed spring in (b). (3 marks)

1. The bicycle pump shown in Figure 7 below is one of the applications of pressure in gases.

Explain how the leather washer functions during;                                   (2 marks)
1. backstroke                                                                                         (1 mark)
As a valve. Pump handle is drawn out as shown.  Volume of air below washer increases and pressure is reduced below atm. pressure.  Air from outside the pump is drawn in.
2. forward stroke                                                                                  (1 mark)
As a piston.
Pump handle is pushed in air, the barrel is compressed.
Or
The pressure of compressed air is greater than the air in the tyre.
1. Explain how greenhouse effect increase the average temperate of the earth.(2 marks)
- Sun’s radiation easily passes through the earth’s atmosphere.
- As it warms up, the earth re-radiates energy of longer wavelength (lower energy/ shorter frequency) which is absorbed by water vapour, CO2 and other gases.
- The warm atmosphere in turn radiates back to the earth so making it warmer than it would otherwise be.

SECTION B (55 MARKS)

1.
1. The figure below shows a planet Venus orbiting the sun in a circular orbit at constant speed.

1. State what provides the centripetal force.                         (1 mark)
Gravitational force.
2. Indicate the direction of centripetal force on the diagram.        (1 mark)
2. A stone is thrown with a horizontal velocity U from the top of a building of height 125m so as to hit a target on the ground 75m from the base of the building as shown below.

Calculate:
1. the time taken for the stone to hit the target.                    (2 marks)

2. the horizontal velocity, u, of the stone.                               (2 marks)
3. A stone of mass 0.5kg is attached to a string of length 0.5m which will break if the tension exceeds 20N.  The stone is whirled in a vertical plane, the axis of rotation being above the ground, as shown in the figure below.

The angular velocity is gradually increased until the string breaks.
1. In what position is the string most likely to break?  Justify.         (2 marks)
Bottom
At the bottom tension is maximum
2. At what angular velocity, w, will the string break?                        (3 marks)

1.
1. Define the term atmospheric pressure.                                         (1 marks)
Is the pressure exerted on the surface of the earth by the weight of the air column.
2. The diagram below shows a hydraulic lift supporting a load of 150kg.  Its cross-sectional areas A1 and A2are 0.02m2 and 0.4m2 respectively.

The length of the effort arm from the length of the plunger from the pivot is 0.4m.
Determine:
1. the pressure exerted by 150kg mass.                                (1 mark)

2. the pressure exerted by F1 on the smaller piston.                        (1 mark)
3750 N⁄m2(Pascal’s Principle)
3. the force F1.                                                                           (2 marks)
4. the applied force, Fe.                                                                        (2 marks)
By principle of moments.
Acm = Cm
Fe ×1m=75N×0.4m
30N
5. the mechanical advantage.                                                   (2 marks)

6. the velocity ratio of the system.                                          (2 marks)
7. the efficiency of the system.                                                 (2 marks)

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