Physics Paper 1 Questions and Answers - Mokasa II Joint Mock Exams 2023

Instructions to candidates

• This paper consists of two sections A and B. Answer all the questions in the spaces provided.
• Electronic silent nonprogrammable calculators may be used.
• Use the following constants where necessary
  g= 10 N/kg
  density of water = 1000kg/m³

SECTION A- 25 MARKS

1. Figure one below shows a Vernier caliper when the jaws are fully closed and when it is used to measure the width of a small wooden block.
   
   Determine the width of the block.        (2 marks)
2.  
   1. Other than the densities of individual liquids, give one more factor on which the density of a mixture of two liquids depend.     (1 mark)
   2. 50cm³ of water (density = 1g/cm³) is mixed with 100cm³ of milk of density 1.2g/cm³.  Determine the density of the mixture    (2 marks)
3. Figure 2 below shows na Bunsen burner.
   
   Explain how the parts labelled M and N make it possible to have an air-gas mixture for ignition at the top of the barrel.      (2 marks)
4.  
   1. Define surface tension and state its SI unit        (2 marks)
   2. Give one advantage of surface tension
5. A barometer reads k cmHg on a certain mountain and m cmHg at sea level. Given that the density of mercury is ρm, that of air is ρa, and gravitational field strength is g, derive an expression to determine the altitude of the mountain.     (2 marks)
6.  
   1. Give one characteristic of Brownian motion that makes it distinct from kinetic theory of matter.    (1 mark)
   2. What conclusion is drawn from the constant random motion of smoke particles as observed in the smoke cell experiment? Explain
      (2 marks)
7. Figure 2 below shows a 2 m long non-uniform plank of wood suspended freely by means of strong threads on both ends A and B.
   
   Given that the tension on A is 20N and the tension on B is 80N, determine
   1. The weight of the plank of wood      (1 mark)
   2. The position of the c.o.g of the plank from end A       (2 marks)
8. Equal masses of water and oil are heated on the same source of heat for the same amount of time. It is observed that oil shows a higher temperature rise than water. Explain.     (2 marks)
9. State and explain the risk a speeding track carrying heavy logs of wood run into when it stops suddenly.
   
   1. Risk............... ( 1mark)
   2. Reason:.......... (1 mark).
10. Figure 3 below is of a velocity time graph for a ball projected vertically upwards on a certain planet P.*
    
    From the graph, determine the acceleration due to gravity on a freely falling object on the planet        (3 marks)

(SECTION B - 55 MARKS)

11.  
    1. Define the term angular velocity    (1 mark)
    2. Explain why satellites set for weather forecast appear stationary to an observer on Earth even though the earth keeps rotating on its own axis.
       (2 marks)
    3. Road banking is a road design meant to allow vehicles negotiate bends at high speeds without the danger of skidding or overturning. How does banking achieve this? (1 mark)
    4. A 2kg mass tied to a 70cm long inextensible string is whirled in a vertical circle as shown at a constant speed of 5 m/s.
       
       1. At what point is the string likely to snap? Explain       (2 marks)
       2. Determine the tension on the string at the positions given below
          1. Position A        (2 marks)
          2. Position B              (2 marks)
12.  
    1. State the law of floatation    (1 mark) 
    2. Explain the upward motion of a hydrogen balloon     (2 marks)
    3. A piece of marble of mass 1.4 kg and relative density of 2.8 is supported by a light string from a spring balance and lowered into a beaker of water standing on a beam balance. Before the stone enters the water, the beam balance reads 5.75kg. Determine:
       1. The reading on the spring balance when the marble is completely immersed        (3 marks)
       2. The reading on the beam balance when the marble is completely immersed      (2 marks)
    4. A wooden block floats in water with ²/₃ of its volume submerged. When placed in oil, ¾ of its volume becomes submerged. Calculate:
       1. The density of the wooden block      (3 marks)
       2. The density of the oil    (2 marks)
13.  
    1. State Charles law
    2. Below is a set-up used to verify Charles' law.
       
       1. State any two function of the part labeled X      (2 marks)
       2. Briefly explain how the set-up can be used to verify Charles' law      (3 marks)
    3. At 25°C, the pressure of a gas is 600mmHg. At what temperature would the pressure be halved?     (3 marks)
14. The figure below shows a hydraulic machine used to lift a load of 300 N. Use it to answer the questions that follow.
    
    A and a are the areas of cross section of the large and small piston respectively. The lengths of the load and effort arms are given as x andy.
    1. Find:
       1. The force F_c given that F_d = 40 N, y = 2m and x= 0.5 m.                    (3 marks)
    2. Calculate the :
       1. Mechanical advantage of the system in (a) above.     (2 marks)
       2. Velocity ratio of the system given that the Area A is 10 times that of a   (3 marks)
       3. The efficiency of the system       (2 marks)
       4. The amount of energy wasted in lifting the load through a height of 2.5 m (3 marks)
15. The figure below shows a simple electrical heater made by a student in the lab.
    
    1. Give reasons why the resistance wire XY is coiled.       (1 mark)
    2. Given that the voltage from the battery is V and current flowing in the circuit is I, show that power is given by P = v²/_R, where R is the resistance of the wire       (2 marks)
    3. An electric heater is made of a wire of resistance 50 ohms and connected to a 230 V mains supply. Determine :
       1. The power rating of the heater.     (2 marks)
       2. The time taken to by the heater to raise the temperature of 300 g of water from 25°C to 80°C.
          (specific heat capacity of water =4200 J/kg/ K)            (3 marks)
    4. Explain how a pressure cooker works           (2 marks)

MARKING SCHEME

1. width = 1.06 − 0.03  ✓
             = 1.03cm  ✓
2.  
   1. Proportion of individual Liquids in the mixture
      T_mix = 50 x 1 + 1.2 x 100 ✓ = 1.133g/cm³   ✓
                        50 + 100
3.  
   • The gas. leaves M at high velocity lowering pressure inside the barrel. ✓
   • The atmospheric pressure outside being higher ✓ pushes air Through N to be mixed with gas.
4.  
   1.  
      • Force that makes the surface of a liquicl behave Like a stretched elastic skin.
      • SI unit - Newton per metre,
   2. Sheltering from rain under an umbrella / Canvas.
5. (M-K) ρm × g = h × ρa × g  ✓
      100
   h =    ρm   (m− k)     ✓
         100ρa
   where h is the altitude of the mountain.
6.  
   1. Brownian motion occur in fluid only while Kinetic theory apply to all states of matter.   ✓
   2.  
      • Particles of matter are in constant random motion.  ✓
      • The air molecules which are in constant random✓ motion are the ones making smoke particles to move so due to uneven bombardment.
7.  
   1. 20N + 80N = 100N    ✓
   2. Let the position be X from A
      100 × x = 80 × 2   ✓
               x = 1.6m   ✓
      Note: Moments is taken about A
8. Oil has lower specific heat capacity than water. ✓Oil thus require less amount of heat for every 1 Kelvin of temperature rise,
9. Risk: Logs may Slide foward above the truck  ✓
   Reason: The logs if not fastened well remain's in a state of motion when the truck suddenly slips.  ✓
   * Award if Newton firsy law is stated as the reason.
10. For free fall
    u = 0m/s
    v = 2m/s
    t = 3 seconds
    g = v − u    ✓
              t
       = 2 − 0   ✓
              3
      = 0.6667m/s²  ✓
    Deny 1 mark if −2 is used on the final velocity
11.  
    1. Rate of Change of angular displacement
    2. They are set in an orbit in which they will have the same period as the earth ✓
    3. Banked roads provide centripetal force from normal reaction ✓ and from friction between ✓ the tyres and the road.
    4.  
       1. C ✓: Point of greatest tension ✓
       2.  
          1. Fe = T + mg
             ∴ T = mv² − mg
                         r
             T = 2 × 5² − 2 × 10  ✓
                      0.7
                =  51.43N  ✓
          2. T = Fe = mv² = 2 × 5²   ✓
                              r         0.7
               = 71.43N  ✓
12.  
    1. A floating object displaces its own weight of the fluid it floats in.  ✓
    2. The balloon displaces equal volume of air as the hydrogen✓. Thus the upthrust created will be greater than the weight hence the upward motion. ✓
    3.  
       1. T_e = W_A  
                  U_W
          2.8 = ¹⁴/_x  ✓
          x = 5N
          Reading = 14 − 5   ✓
            = 9N   ✓
       2. Reading = 5.75 + mass of displaced water due to the upthrust created.
                         = 5.75 + 5  ✓
                         = 6.25kg   ✓
    4.  
       1. Relative density = ²/₃  ✓
          Density of sound = ²/₃ × 1000 ✓ (Relative density × density of water)
                                      = 666.7kg/m³ ✓
       2. T_solid   = ¾
            T_oil 
          666.7 = ³/₄ 
            Toil
          Toil = ⁴/₃ × 666.7 ✓ = 888.9kg/m³  ✓
13.  
    1. The Volume of a fixed mass ✓ of a gas is directly proportional to its absolute temperature at constant pressure
       Deny vαT
    2.  
       1.  
          • Dry the air
          • Act as an index
          • Trap to the air
       2.  
          • Height of the air column is recorded at room temperature then heating is done where stirring. 
          • Values of height of air column are then nrecorded at regular intervals of temperature. ✓
          • A graph of height against absolute temperature is plotted. ✓
          • A straight line through the origin is obtained ✓ showing that volume is proportional to temperature.
    3. P₁ = m600mmHg
       T₁ = 298K
       P₁   = P₂     ✓
       T₁      T₂
       P₂ = 300mmHg
       T₂ =  ?
       600 = 300      ✓
       298     T₂ 
       T₂ = 149K    ✓
             = −126°C
14.  
    1.  
       1. F_c × 2 = 40 × 0.5   ✓
          F_c = 10N   ✓
    2.  
       1. M.A = ^L/_E = ³⁰⁰/₁₀ = 30    ✓
       2. V.R_T = V.R_L × V.R_H   ✓
                   = ²/_0.5 × ^10a/_a  ✓
                  = 40   ✓
       3. η = M.A  × 100
                 V.R
             = ³⁰/₄₀ × 100   ✓
             = 75%  ✓
       4. Useful work done corresponds to 75%
          Energy wasted = ²⁵/₇₅ × 300 × 2.5    ✓
                                  = 250J   ✓
15.  
    1. To increase the effective length of the wire.   ✓
    2. P = IV
       But I = ^V/_R
       Hence P = (^V/_R) × V   ✓
                    = V²    ✓
                        R
    3.  
       1. P = 230²
                  50
             = 1058W
       2. Pt = mcθ
          1058t = 0.3 × 4200 × 55   ✓
          t = 65.50 seconds   ✓
    4.  
       • Trapped steam builds up pressure ✓ raising the boiling point of water.
       • Food thus cooks at higher temperature hence softening faster.   ✓