KCSE 2015 Physics Paper 1 with Marking Scheme

SECTION A (25 marks)
Answer all the questions in this section in the spaces provided.

1. Figure 1 shows part of the main scale of the vernier callipers.
   
   Figure 1
   Insert the vernier scale to the main scale, to show a reading of 3.14cm. (1 mark)
2. Figure 2 (a) shows the initial reading of a burette used to measure the volume of oil. After 50 drops of the oil were run out, the final reading was shown in figure 2 (b).
   
   Determine the volume of the drop of oil. (2 marks)
3. A spring extends by 6 cm when supporting a mass of 0.06 kg on earth. When the spring is used to support the same mass on the moon, it extends by 1 cm. Determine the moon's gravitational strength.(Take gravitational field strength on earth as 10 Nkg^-1)
4. State two factors that detemine the pressure at a point in a liquid. (2 marks)
5. A student wearing a sharp pointed shoe is likely to damage a soft wooden floor. Explain. (2 marks)
6. Figure three shows arrangement of molecules in the three states of matter.
   
   1. Name the process represented by the arrow.(1 marks)
   2. State the reaction for the arrangement of molecules in state 3.(1 marks)
7. Two containers A and B of equal dimensions but different metals are fitted with identical glass casings. The two containers initially at the same temparature are simultaneously filled with boiling water. It is observed that the glass casing on A breaks earlier than the one on B. Explain this Observation.(2 marks)
8. Figure 4 shows a uniform metal rod balanced at its centre by different forces.
   Determine the value of T.  (3marks)
9. Figure 5 shows air flowing through a pipe of different cross-sectional areas.Two pipes A and B are dipped into water.
   
   Explain the cause of the difference in the levels of water in the pipes A and B.(2 marks)
10. A balloon is filled with hydrogen gas and then released into the air. It is observed that as it rises higher into the air it expands. Explain why it expands.  (2 marks)
11. A person carrying a heavy luggage using one hand leans away from the luggage. State the reason for this.  (1 marks)
    
12. Figure 6 shows a glass tube with water fitted with two identical thermometers A and B.It is heated as shown.
    State with a reason which one of the two thermometers shows a higher temparature.(2 marks)
13. Mechanics is one of the branches of physics .State what it deals with (1 marks)

(SECTION B:  55 MARKS)
Answer ALL questions in this section in the spaces provided

14.     
    1. Figure 7(drawn to scale) shows a section of tape after passing through a ticker timer opperated at a frequency of 50Hz. The tape is attached to a trolley moving in the direction shown.
       
       1. Determine the velocity between:
          1. P and Q; (4 marks)
          2. X and Y. (2 marks)
       2. Determine the acceleration of the trolley(3marks)
    2. Two bodies of masses 5kg and 8kg moving in the same velocities 20 ms^-1 and 15 ms^-1 respectively collide inelastically. Determine the velocity of the bodies after the collision. (4 marks)
15.    
    1. Figure 8 shows a 200g mass placed on a frictionless surface and attached to a spring.
       
       The spring is compressed and released. Given that the elastic potential energy of the compressed spring is 2.7 x 10^-2 J, determine the maximum speed the block moves after it is released.(4 marks)
    2. In a wheel and axle system, state the advantage of having a large wheel diameter compared to the axle diameter for a frictionless system.(1 marks)
    3. A body is released from a height h. Sketch a graph of potential energy against kinetic energy as the body falls to the ground.(2 marks)
    4. Figure 9 shows a hydraulic lift system. The radius of the small piston is 3cm while that of the larger piston is 9cm. A force of 90 N is applied to the smaller piston.
       
       Determine the:
       1. Maximum load that can be lifted.(3marks)
       2. Effeciency of the system.(3marks)
16.    
    1. Figure 10 shows an incomplete set up that can be used in an experiment to determine the specific heat capacity of a solid mass M by electrical method.
       
       1. Complete the diagram by inserting the missing components for the experiment to work.(2 marks)
       2. Other than temparature, state three measurements that should be taken.(3marks)
       3. The final temparature was recorded as 0. Write an expression that can be used the specific heat capacity of the solid. 2marks)
    2. State three ways of increasing the sensitivity of a liquid in a glass thermometer.(3 marks)
17.    
    1. Figure 11 shows a graph of preassure (p) against volume(v) in a fixed mass of gas at constant temparature.
       In the spaces provided, sketch the corresponding graph of p against 1/v.(1 marks)
    2. Explain the pressure law using the kinetic theory of gases.(3 marks)
    3. 20 cm³ of gas exerts a pressure of 70 mmHg 25⁰C. Determine the temparature of the gas when the temperature increases to 900mmHg and the volume to 15 cm³. (4 marks)
    4. Figure 12 shows the path of a light ball projected horizontally.
       
       The ball is then made to spin in an anticlockwise direction as it moves:
       1. On the same axis, sketch the new path of the ball. (1 marks)
       2. Explain how the balll attains the new path. (2marks)
18.    
    1. Figure 13 shows a pendulum bob suspended by a thread moving in a horizontal circle.
       
       1. Name two forces acting on the pendulum bob as it moves. (2 marks)
       2. State what happens to each of the forces when the angular velocity of the pendulum bob is increased. (2 marks)
       3. State two applications of uniform circular motion in daily life. (2 marks)
    2. Figure 14 shows a block floating in water.
        
       When the water is heated; it is observed that the block sinks further. Explain this observation. (2 marks)

MARKING SCHEME

SECTION A

1. 
   
   Correct reading (1)
2. Volume = 21 - 19
   = 2 cm³
   Volume of 1 drop = 2 = 0.04 cm³ 
                               50
3. Mg_e = Ke_e  K = Mg_e 
                           e_e
   Mg_m = Ke_m (K is constant)
   Mg_m =Mg_e.e_m
              e_e
   g_m = g_e.e_m – 10 x 0.01 = 1.67NKg^-1 (3)
             e_e           0.06
4.    
   • depth
   • density of the liquid
   • gravitational field strength
5. The sharp heeled shoe exerts great pressure v due to small surface area of contact
6.    
   1. freezing 
   2. The intermolecular forces are weaker
7. Both containers have a greater V expansion compared to glass, but A expands faster than B
8. Sum of anti clockwise moments = sum of clockwise moments ✓
   4 x 35 + T x 50 = 8 x 40
   140 + 50T = 320 
   T= 320 - 140
             50
   3.6 N 4
9. The velocity of air above B is greater than that above AV decreasing the pressure above B hence the water rises higher in B
10. As the balloon rises, the atmospheric pressure reduces v hence the pressure due to the hydrogen gas pushes the walls of the balloon to expand 
11. To maintain stability
12. B  ✓
    As the heating continues the hot water rises conventionally, due to the reduced density the hot water remains at the top. (2)
13. Study of motion of bodies under the influence of forces.

SECTION B

14.    
    1.    
       1. Measurement of length PQ = 3 cm
          T =  1  = 0.02 Sec
                50
          Vpq =  3  = 150 cm s^-1
                  0.02
       2. Vxy= 0.5 
                 0.02
          25 cm s^-1
       3. a = final velocity – initial velocity
                            time taken
           25 – 150 
          5 x 0.002
          =-1250 cm s^-2
    2. Momentum before collision = Momentum after collision
       M₁U₁+M₂U₂ = V(M₁ + M₂)
       5 x 20 +8 x 15 = V(5+8)
       220 = 13V
       V= 220
             13
       16.92 ms^-1
15.    
    1. K.E. = P.E.
       ½ mV² =00.027
       ½ x 0.2 x V² = 0.027
       V = 2 x 0.27
                0.2
       V = 5.196 MS^-1
    2. Reduces the effort required to raise the V load (increases the mechanical advantage.) (1)
    3. 
       
    4.    
       1.  F ₁ = F₂
           A₁     A₂ 
           90  =  F₂
          π.3²   π.9²
          F₂ = π.9² .90
                    π.3²
          = 810N
          • Straight line with negative gradient v
          • axis touched V
       2. Efficiency = MA  x 100%
                            V.R
          MA=  L   =810= 9 
                  E      90
          V.R = 81  = 9
                   9
          Efficiency = 9 x 100%=100%
                           9
16.    
    1.      
       1. ammeter in series ✓
          voltmeter in parallel ✓
       2.    
          • ammeter reading (current)
          • voltmeter reading (voltage)
          • time
       3. Electrical energy supplied = heat gained by solid
          Vit = mc (θ - Θ₁)
          or C =      Vit      
                   mc (θ - Θ₁)
    2.    
       • reduce the diameter of the bore
       • use a thin walled bulb
       • use a liquid with a high expansivity 
17.    
    1. 
       
       a straight line through the origin (1)
    2.  P constant at constant volume
        T
       as temperature increases, the kinetic energy of the molecules increases V causing more collisions hence increased pressure.
    3. P₁V₁ = P₂V₂
         T₁        T₂
       760 x 20 = 900 x 15
          298             T₂
       T₂ = 900 x 15 x 298
                  760 x 20
       = 264.67 K
    4.      
       1. 
          
       2. Spinning causes high velocity of air above v the ball hence reduced pressure which causes the ball to rise higher.
18.    
    1.       
       • Tension (T)
       • Weight (Mg)
    2. Tension - increases
       Weight - remains constant
    3.    
       • Centrifuges
       • Speed governors
       • Merry-go-rounds
         (any other relevant two correct)
    4. When heated the density of the water decreases V hence block sinks further V as it displaces more volume of water.