KCSE 2017 Physics Paper 1 with Marking Scheme

INSTRUCTIONS TO CANDIDATES

• This paper consists pf two sections: A and B
• Answer all questions in section A and B.
• All working MUST be clearly shown where necessary.
• Non-programmable silent electronic calculator may be used.
• Candidates should answer the questions in English

SECTION A: (25 marks)

Answer all the questions in this section in the spaces provided.

1. In order to determine the size of an oil molecule, a student performed an experiment using five oil drops to make a circular patch of the oil on the surface of water in a waterbath. State two assumptions made by the student during the calculations.   (2 marks)
2. In an experiment to determine the density of Liquid R, a student obtained the followed data:
   • Mass of an empty density bottle = 55.0 g 
   • Mass of the density bottle + water = 80.0 g
   • Mass of the density bottle + Liquid R = 70.0 g
     Determine the density of Liquid R. (density of water is 1000 kgm³ )      (3 marks)
3. It is observed that when 20cm³ of alcohol is mixed with 20cm³ of water, the volume of the mixture is 39 cm³. State a reason why the volume of the mixture is not 40cm³       (1 mark)
4. When a liquid is heated in a glass flask, it is observed that the level at first goes down and then rises. Explain this observation.   (2 marks)
5. Figure 1 shows a uniform wooden bar at equilibrium with two cans Y and Z of equal mass but different diameters.
   
   The cans are simultaneously filled with equal volumes of water.
   Explain the observation made.    (2 marks)
6. State the reason why the speed of water at the narrow section of a river is higher than at the wider section.   (1 mark)
7. A stone is thrown vertically upwards. Sketch a graph of potential energy (y axis) against time as the stone moves until it hits the ground.   (1 mark)
8. Using the definition of impulsive force, show that F=ma (3 marks)
9. Figure 2 shows a round bottomed flask fitted with a long capillary tube containing a drop of coloured water.
   
   The flask is immersed in ice water for sometime. State the observation made.   (2 marks)
10. State one assumption for the experiments carried out to verify the gas laws.   (1 mark)
11. A student who wanted to take a bath mixed 4 kg of water at 80°C with 6 kg of water at 20°C. Determine the final temperature of the water.     (3 marks)
12. A uniform metre rule is pivoted at its centre. Two weights of 20 N and 10N are suspended at the 20cm and 100cm marks respectively. Determine the position at which a 10N weight should be suspended in order to balance the system.     (3 marks)
13. Figure 3 shows two possible designs of a three legged stool.
    
    State a reason why B is more stable than A.     (1 mark)

SECTION B: (55 marks)

Answer all the questions in this section in the spaces provided.

14.  
    1. A tape attached to an accelerating trolley passes through a ticker timer that makes dots on it at a frequency of 50 Hz. The ticker timer makes 10 dots on a 10cm long tape such that; the distance a between the first two dots is 0.5 cm and the distance b between the last two dots is 1.5 cm.
       
       1. Determine the velocity of the trolley at:
          1. distance a   (4 marks)
          2. distance b.   (2 marks)
       2. Determine the acceleration of the trolley.     (3 marks)
    2. State with a reason what would be observed on the spacing between the dots on the tape when the trolley is made to move on a horizontal surface.   (2 marks)
15.  
    1. A student was provided with several identical masses, a metre rule, a spring and a stand, boss and clamp. Outline five steps that the student should follow in order to verify Hooke's law.  (5 marks)
    2. Figure 4 shows a graph that was rwan from the results obtained in an experiment to study the extension of a spring.
       
       From the graph determine;
       1. The spring constant ,   (3 marks)
       2. The load that causes an extension of 3 x 10⁻² m.    (1 mark)
    3. Three identical springs of spring constant 100⁻¹ Nm' are arranged as shown in Figure 5 to support a 5 N load.
       
       Determine the total extension in the arrangement.    (3 marks)
16.  
    1. In an experiment to determine the size of an oil molecule, oil is placed on the surface of water after sprinkling lycopodium powder on it.
       1. State two reasons why oil is used.  (2 marks)
       2. State the function of the lycopodium powder.    (1 mark)
       3. State any two assumptions that are made in this experiment.     (2 marks)
       4. Explain why the oil spreads on the surface of water.     (2 marks)
    2. The following data was obtained from an experiment to determine the size of a palm oil molecule.
       • Volume of 100 drops of palm oil = 15.0 mm³
       • Area of a patch from one drop of oil = 8.0 x 10⁴ mm²
         Determine the size of a palm oil molecule.    (3 marks)
17.  
    1. State the law of flotation.   (1 mark)
    2. Figure 6 shows two solids W and X made of the same material and immersed in water.
       
       1. State with a reason which one of the containers experiences a greater upthrust,   (2 marks)
       2. Solid W weighs 12 N in air, 2N in water and 4 N in another liquid. Determine the density of the other liquid.   (3 marks)
    3. Figure 7 shows two identical wooden blocks each of mass 0.2 kg suspended in water by two strings M and N.
       
       Given that the upthrust on each block is 3.2 N, determine the tension in string:
       1. M    (2 marks)
       2. N     (2 marks)
    4. State any one application of hydrometers.    (1 mark)
18.  
    1. Figure 8 shows part of a hydraulic brake system.
       
       Describe how the system works.   (5 marks)
    2. State three conditions necessary for a driver to negotiate a bend on a flat level road at a relatively high speed. (3 marks)
    3. Figure 9 shows two identical cans U and V each with a small opening at the top. Different amounts of water were put into the cans and heated until the water strated to boil.
       
       Explain what will be observed when both cans are then suddenly dipped into a cold waterbath.   
       (3 marks)

MARKING SCHEME

1.  
   • The patch was monolayer. ✓
   • The patch was a perfect cylinder. ✓
   • Molecular diameter is uniform.
   • The patch is a perfect circle.     (2 marks)
     (Any two correct)
2. Relative density = 70 − 55  ✓
                              80 − 55
                           = 0.6✓
   Density =0.6 x 1000
              = 600 kgm⁻³ ✓
   OR Volume of water = ²⁵/₁ = 25cm³
    = Volume of R. = 25cm³ ✓
   Mass of R = 70 − 55 = 15g  ✓
   p = ^m/_v = ¹⁵/₂₅ = 0.6gcm⁻³ ✓   (3 marks)
3. Spaces between the water molecules are occupied by the alcohol molecules. ✓  (1 mark)
4. The flask expands first before ✓ the liquid. Then the liquid expands more. ✓  (2 marks)
5. The wooden bar remains in equilibrium. the weight remains the same on both sides. Hence turning effect is the same✓to the edge causing a bigger turning effect (moments).✓  (2 marks)
6. To conserve mass - (A₁V₁ = A₂V₂) ✓/ ensure the volume flux is constant.  (1 mark)
7.  
     (1 mark)
8. Impulse = (Ft) = change in momentum
                     Ft = mv − mu.  ✓
                      F = mv − mu = m(v−u) ✓
                                  t               t
                   but = v − u = a
                               t
                      F = m.a  ✓        (3 marks)
9. The drop first rises then falls   (2 marks)
10. The gas is ideal gas  (1 mark)
11. Heat lost by hot water = heat gained by cold water  ✓  
                    mcΔθ(hot) = mcΔθ (cold)
             4 x C x (80−t) = 6 x C x (t−20)  ✓
                             10t =-440
                                t = 44°C ✓   (3 marks)
12. 20 × 30 = 10 × 50+ x × 10 ✓
             x = 600−500 ✓
                        10
               = 10
               = 60cm mark. ✓  (3 marks)
13. The weight of the body is such that the net position of the center of gravity in B is lower than in A, hence B is more stabler. ✓  (1 mark)
14.  
    1.  
       1.  
          1. V_a = ^d/_t ✓,   t = ¹/₅₀ = 0.02sec ✓
             = 0.5   ✓
                0.02
             = 25cms⁻¹ ✓   (4 marks)
          2. V_b = ^d/_t 
             = 1.5 
                0.02
             =75cms⁻¹ (2 marks)
       2.  
          
          =  75 − 25
              8 × 0.02
          = 312.5cms⁻² (3 marks)
    2.  
       • The spacing reduces ✓ with time.
       • The trolley decelerates with time on a horizontal surface. ✓  (2 marks)
15.  
    1.  
       • Hung the spring on the stand and note the position of the pointer using the metre rule.
       • Suspend a mass on the spring and note the new position of the pointer
       • Increase the load in steps and record the position of the pointer for each load.
       • Draw a table of weight against extension 
       • Plot a graph of force against extension.  (5 marks)
         (Correct steps 5 x 1)
    2. From the graph 
       1. K = gradient ✓
             = ΔF = 0.9 − 0.5 =     0.4       ✓
                Δe       7 − 4       (3 × 10⁻²)
           K = 1.33 x 10²Nm⁻¹ ✓   (3 marks)
       2. Load = 0.38N ✓ (1 mark)
    3. e = ^F/_K = ⁵/₁₀₀ = 0.05 m for cach spring. ✓
       ∴lower spring = 0.05m
       Upper springs = 0.05  = 0.025 ✓
                                 2
       Total = 0.05 + 0.025
               = 0.075 m ✓  (3 marks)
16.  
    1.  
       1.  
          • Oil doesn't mix with water. ✓
          • Oil is less dense hence floats on the water surface. ✓  (2marks)
       2. To show boundary of the oil patch clearly, for measurements to be taken. ✓ (1 mark)
       3.  
          • The oil drops is a perfect sphere. 
          • The patch is monolayer. 
          • The patch is a perfect circle. 
          • Molecular diameter is uniform.
            (any two correct)   (2marks)
       4.  
          • The oil breaks the surface tension ✓ making the patch to form a perfect circle.✓ 
            (2marks)
    2. Volume of 1 drop = ¹⁵/₁₀₀ = 0.15mm² ✓
       Volume of drops = Volume of oil patch.
       ⁴/₃πr³ = πr²h = 15.0 mm³ ✓
       Thickness of molecule h =   0.15    
                                             8.0 x 10⁴
                                           = 1.875 x 10⁻⁶ mm
                                           ≃ 1.9 x 10⁻⁶ mm ✓    (3 marks)
17.  
    1. A floating body displaces its own weight of the fluid in which it floats.  (1 mark)
    2.  
       1. X✓ - It has a larger volume.✓ /Displaces a larger volume of water.  (2 marks)
       2. Relative density = Upthrust in liquid ✓
                                     Upthrust in water
                                  = 12− 4 = 8  ✓
                                      12−2    10
                                   = 0.8 kgm⁻³ ✓  (3 marks)
    3.  
       1. Tension in M = 3.2−2 ✓
                            = 1.2N ✓  (2 marks)
       2. Tension in N =(3.2−2) + 1.2
                            = 1.2 + 1.2 ✓
                            = 2.4N ✓   (2 marks)
    4. Measuing the relative density of liquids  ✓   (1 mark)
18.  
    1.  
       • The driver applies a force on the pedal. ✓
       • This force transmits pressure to the master cylinder fluid. ✓
       • Equal pressure is transmitted to the wheel cylinder causing the pistons of the wheel cylinder to push brake shoe hence✓
       • Pressing the brake pads that in turn press the wheel reducing its rotation. ✓
       • When the applied force is removed, the return spring pulls back the shoe and pistons to the original position ✓  (5 marks)
    2.  
       • Higher friction ( wider tyres, rougher road)
       • Lower radius
       • Higher mass     (3 marks)
    3.  
       • U is observed to crush. 
       • It has more steam which when cooled creates a greater ✓ vacuum hence pressure causes ✓ collapsing.   (3 marks)