Physics Paper 1 Questions and Answers - Form 4 End Term 1 Exams 2021

PHYSICS
FORM 4
END TERM EXAMS
TERM 1 2021
PAPER 1
TIME 2 ½hrs

INSTRUCTIONS

• This paper consists of 2 sections: A and B
• Answer all the questions in these sections
• Mathematical tables and calculators may be used.

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

1. The figure below shows the scale of a measuring instrument when measuring the thickness of an object.
   
   Figure 1
   1. Name the instrument to which the scale belongs. (1 mark)
   2. Find the reading of the instrument shown. (2 marks)
2. A solid weighs 32.5N on the surface of the moon. The force of gravity on the moon is 1.7Nkg-1. Determine the mass of the solid. (3 marks)
3. A mercury barometer reads 760mmHg at sealevel and 700mmHg at the top of a mountain. If the density of mercury is 13,600kg/m3 and average density of air is 1.30kg/m3, calculate the height of the mountain. (3 marks)
4. Briefly explain why rooms are at a lower level and ventilators at a higher level. (2 marks)
5. State the Archimedes principle. (1 mark)
6. Figure 2 below shows a piece of wood fitted into a copper pipe and a piece of paper wrapped tightly around the junction.
   Explain why the side of the paper around wood burns first when flame is applied at the junction. (2 marks)
   
   Figure 2
7. State why it is necessary to leave an air space in closed glass bottle of water when it is to be kept in a refrigerator. (1 mark)
8. A student pulls a block of wood along a horizontal surface by applying a constant force. State the reason why the block moves at a constant. (1 mark)
9. The efficiency of a pulley system is always less than 100%. State two reasons. (2 marks)
10. Figure 3 shows a small toy boat floating on water in a basin. X and Y are two points near the toy.
    
    Figure 3
    When a hot metal rod is dipped into the water at point X the toy is observed to move towards Y.Explain this observation. (2 marks)
11. How much current is taken by a bulb whose rate is 100 and which is designed for mains supply of 240V? (3 marks)
12. What is the gravitational potential energy stored in a spring when stretched through 4cm by a force of 2N. (2 marks)

SECTION B (55 MARKS)
Answer ALL the questions in this section in the spaces below.

13.      
    1. Define centripetal acceleration. (1 mark)
    2. Distinguish between angular and linear velocity. (2 marks)
    3. The figure 4 below shows an object of mass 0.2kg whirled in vertical circle of radius 0.5m at uniform speed of 5m/s.
       
       Determine the tension of the string at;
       1. Position A. (3 marks)
       2. Position B. (3 marks)
       3. At what point is the string likely to cut. Explain. (2 marks)
14.    
    1. Explain why it is advisable to use the pressure cooker for cooking at high altitudes. (2 marks)
    2. Water of mass 3kg initially at 20℃ is heated in an electric kettle rated 3.0kW. Thewater is heated until it boils at 100℃. Taking specific heat capacity of water=4200Jkg/K, heat capacity of kettle=450J/kg, specific latent heat of vapourisation of water =2.3MJ/kg, calculate;
       1. The heat absorbed by the water. (2 marks)
       2. Heat absorbed by the electric kettle. (2 marks)
       3. The time taken for the water to boil . (2 marks)
       4. How much longer it will take to boil away all the water? (3 marks)
15.    
    1. A ball is dropped from the top of a vertical cliff 45m high. Given that the velocity just before striking the sandy beach is 30m/s, and the ball penetrate the sand to a depth of 10cm determine its average retardation. (3 marks)
    2. The figure below shows a force distance graph for a car being towed on a level ground.
       
       1. Calculate the total work done. (2 marks)
       2. If the velocity just before reaching C is 0.6 m/s. Calculate the power developed by the engine at this point. (2 marks)
16.    
    1. State the pressure law; (1 mark)
    2. Explain how a gas exerts pressure. (2 marks)
    3. The figure below shows a set up used to verify pressure law.
       
       1. State the measurement that may be taken in the experiment. (2 marks)
       2. Explain how the measurement in (i) above may be used to verify pressure law. (2 marks)
       3. A car tyre is at pressure of 5.0x105 Pa at a temperature of 37℃. While it is running the temperature rises to 75℃. What is the new tyre pressure?(Assume the tyre does not expand) (3 marks)
17.    
    1. State the law of conservation of energy. (1 mark)
    2. The diagram below shows a pulley system, a mass of 10kg is raised 2m by an effort of 80N.
       
       1. Calculate the distance moved by effort. (2 marks)
       2. How much potential energy does the load gain? (1 mark)
       3. How much work is done by the effort? (1 mark)
       4. What is the efficiency of these pulleys? (2marks)
       5. Explain why it easier to tighten or loosen a nut using a spanner with a long handle than one with a short handle. (1 mark)
18. A stone of mass 4.0kg immersed in water and suspended from a spring balance with a string. The beaker was placed on a compression balance whose reading was 85N. The density of the stone was 3000kg/m-3while the density of the liquid was 800kg/m-3. Determine the;
    1. Volume of the liquid displaced. (2marks)
    2. Upthrust on the stone. (4marks)
    3. Reading on the spring balance.

MARKING SCHEME

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

1. The figure below shows the scale of a measuring instrument when measuring the thickness of an object.
   
   Figure 1
   1. Name the instrument to which the scale belongs. (1 mark)
      • Vernier calliper
   2. Find the reading of the instrument shown. (2 marks)
      • Main scale 5.00
        Vernier scale (2 x 0.01) = 0.02
        5.00 + 0.02 = 5.02 cm
        
        
2. A solid weighs 32.5N on the surface of the moon. The force of gravity on the moon is 1.7Nkg-1. Determine the mass of the solid. (3 marks)
   • M = ^w/_g
     = ^32.5/_1.7
     = 19.117 kg / 19.12 kg
     
     
3. A mercury barometer reads 760mmHg at sealevel and 700mmHg at the top of a mountain. If the density of mercury is 13,600kg/m³ and average density of air is 1.30kg/m³, calculate the height of the mountain. (3 marks)
   • Difference in pressure 760 – 700 = 60mm
     ⁶⁰/₁₀₀₀ x 13600 x 10 = h x 1.3 x 10
     h=⁸¹⁶⁰/_{(1.3 ×10)}
     h=627.69 m
     
     
4. Briefly explain why rooms are at a lower level and ventilators at a higher level. (2 marks)
   • Warm air being lighter raises and escapes through the ventilators while the colder air gets in through the windows and doors. 
     
     
5. State the Archimedes principle. (1 mark)
   • When a body is partially or totally immersed in a fluid, it experiences an upthrust equal to the weight of the fluid displaced. 
     
     
6. Figure 2 below shows a piece of wood fitted into a copper pipe and a piece of paper wrapped tightly around the junction.
   Explain why the side of the paper around wood burns first when flame is applied at the junction. (2 marks)
   
   Figure 2
   
   • Wood being a poor conductor of heat does not allow the excess heat so it gets charred
     
     
7. State why it is necessary to leave an air space in closed glass bottle of water when it is to be kept in a refrigerator. (1 mark)
   • Air space is to allow for expansion of water when it freezes preventing the glass bottle from breaking
     
8. A student pulls a block of wood along a horizontal surface by applying a constant force. State the reason why the block moves at a constant. (1 mark)
   • Frictional force is equal to the applied force but in opposite direction. The net applied force is zero.
     
     
9. The efficiency of a pulley system is always less than 100%. State two reasons. (2 marks)
   
   • Friction between moving parts of the pulley system / friction.
     Weight of the movable part of pulley // work done in lifting the moving parts of pulley system.
     
     
10. Figure 3 shows a small toy boat floating on water in a basin. X and Y are two points near the toy.
    
    Figure 3
    When a hot metal rod is dipped into the water at point X the toy is observed to move towards Y.Explain this observation. (2 marks)
    • The hot metal rod breaks the surface tension of the water; surface behaving like stretched skin is pulled towards Y.
       
11. How much current is taken by a bulb whose rate is 100Ω and which is designed for mains supply of 240V? (3 marks)
    • P = IV 
      I = ^P/_V 
      = ¹⁰⁰/₂₄₀ 
      = 0.42 A 
      
      
12. What is the gravitational potential energy stored in a spring when stretched through 4cm by a force of 2N. (2 marks)
    • P.E = ^Fe/₂
      = ^{(2 ×0.04)}/₂ 
      =0.04 Joules 

SECTION B (55 MARKS)
Answer ALL the questions in this section in the spaces below.

13.      
    1. Define centripetal acceleration. (1 mark)
       • This is a force that maintains a body in circular motion and directed towards the centre 
         
         
    2. Distinguish between angular and linear velocity. (2 marks)
       • Angular velocity is rate of change of angular displacement  with time while linear velocity is rate of change of linear displacement with time.
         
         
    3. The figure 4 below shows an object of mass 0.2kg whirled in vertical circle of radius 0.5m at uniform speed of 5m/s.
       
       Determine the tension of the string at;
       1. Position A. (3 marks)
          • T = MV²/r-mg
            = (0.2 × 5²/0.5)- (0.2 ×10) 
            = 10 – 2 = 8N
            
            
       2. Position B. (3 marks)
          • T = MV²/r
            = (^{(0.2 × 25)}/_0.5)
            T = 10N
       3. At what point is the string likely to cut. Explain. (2 marks)
          • At C, because tension is high at 12N
            T = ^_MV2/_r+mg
14.    
    1. Explain why it is advisable to use the pressure cooker for cooking at high altitudes. (2 marks)
       • At high altitude there is low pressure; this lowers the pressure cookers raising the boiling point and more heat is absorbed and food cooks faster
         
         
    2. Water of mass 3kg initially at 20℃ is heated in an electric kettle rated 3.0kW. Thewater is heated until it boils at 100℃. Taking specific heat capacity of water=4200Jkg/K, heat capacity of kettle=450J/kg, specific latent heat of vapourisation of water =2.3MJ/kg, calculate;
       1. The heat absorbed by the water. (2 marks)
          • Q = MCΔθ
            = 3kg x 4200JKg^-1k^-1 x 80 
            = 240 x 4200 = 1008000J / 1.008kJ 
            
            
       2. Heat absorbed by the electric kettle. (2 marks)
          • Q = M_kC_kΔθ
            = 450 x 80  = 36000J
            
            
       3. The time taken for the water to boil . (2 marks)
          • pt = total heat absorbed
            pt = 36000 + 10080001
            3000t = 1044000
            t = 1044000/3000
            t = 348 sec
            
            
       4. How much longer it will take to boil away all the water? (3 marks)
          • pt = mLv
            3000t = 3 x 2.3 x 10⁶
            t = (3 ×2.3 × 10⁶)/3000
            t = 2300 seconds
15.    
    1. A ball is dropped from the top of a vertical cliff 45m high. Given that the velocity just before striking the sandy beach is 30m/s, and the ball penetrate the sand to a depth of 10cm determine its average retardation. (3 marks)
       • v² = u² + 2as 
         O² = 900² + 2 x a x 0.10
         -900 = 0.20 a
         a = ^(-900)/_0.20
         a = -450 m/s²  (negative a must)
         
         
    2. The figure below shows a force distance graph for a car being towed on a level ground.
       
       1. Calculate the total work done. (2 marks)
          • Total work done = Area under graph 
            ( ½ x 4 x 600) + (600 x 4) + (½ x 2 x 600) + (2 x ½ x 600)
            1200 + 2400 + 600 + 600
            = 4800 J
            
            
       2. If the velocity just before reaching C is 0.6 m/s. Calculate the power developed by the engine at this point. (2 marks)
          • P = force x velocity
            = 0.6 m/s x 600
            = 360 W
16.    
    1. State the pressure law; (1 mark)
       • The pressure of a fixed mass of gas is directly proportional to absolute temperature provided that volume is kept constant. 
         
         
    2. Explain how a gas exerts pressure. (2 marks)
       • When a gas is heated it expands increasing the number of collusions per unit area which in turn raise the pressure
         
         
    3. The figure below shows a set up used to verify pressure law.
       
       1. State the measurement that may be taken in the experiment. (2 marks)
          • Temperature of water
          • Pressure gauge reading
            
            
       2. Explain how the measurement in (i) above may be used to verify pressure law. (2 marks)
          • Collect various values of pressure under different temperatures
          • Plot a graph of pressure against temperature and study the values
            
            
       3. A car tyre is at pressure of 5.0x105 Pa at a temperature of 37℃. While it is running the temperature rises to 75℃. What is the new tyre pressure?(Assume the tyre does not expand) (3 marks)
          • P α T →P=KT →K=P/T
            P1 – 5.0 x 105 Pa
            P2 = ?
            T1 = 273 + 37 = 300k
            T2 = 75 + 273 = 348k
            P₁/T₁ = P₂/T₂ 
            ⁵⁰⁰⁰⁰⁰/₃₀₀= P₂/348 
            P2 = ^{(500000 ×348)}/₃₀₀
            = 580000
            P2 = 5.8 x 105 Pa
17.    
    1. State the law of conservation of energy. (1 mark)
       • The sum of kinetic energy and potential energy of a system is constant
         Or
       • Energy can neither be created nor destroyed but can be transformed from one form to another
         
         
    2. The diagram below shows a pulley system, a mass of 10kg is raised 2m by an effort of 80N.
       
       1. Calculate the distance moved by effort. (2 marks)
          • V.R = 2 = ^{(Distance moved by load)}/_{(Distance moved by effort)}
            2 = ^x/₂
            2x = 2m
            x = 1m
            
            
       2. How much potential energy does the load gain? (1 mark)
          • P.E = mgh
            = 10 x 10 x 2
            = 200J
            
            
       3. How much work is done by the effort? (1 mark)
          • Work input = Effort x Effort distance
            = 80N x 1m
            = 80 Joules
            
            
       4. What is the efficiency of these pulleys? (2marks)
          • MA/VR x 100% = efficiency
            (¹⁰⁰/₈₀)/2 x 100% = ⁵⁰⁰⁰/₈₀
            Eff = 62.5%
            
            
       5. Explain why it easier to tighten or loosen a nut using a spanner with a long handle than one with a short handle. (1 mark)
          • With long handle spanner the effort used is less than short handle spanner so one does a lot of work 
            
            
18. A stone of mass 4.0kg immersed in water and suspended from a spring balance with a string. The beaker was placed on a compression balance whose reading was 85N. The density of the stone was 3000kg/m^-3while the density of the liquid was 800kg/m^-3. Determine the;
    1. Volume of the liquid displaced. (2marks)
       • V = ⁴/₃₀₀₀ 
         V = 1.33 x 103m³  (At least 2 d.p)
         
         
    2. Upthrust on the stone. (4marks)
       • Upthrust = Weight of liquid displaced = vρg
         Liquid; 800 x 1.33 x 10³ x 10
         = 10.64 N
         Upthrust in water = v
         1.33 x 103m³ x 10 x 1000
         = 13.33N 
         
         
    3. Reading on the spring balance.
       • Weight of stone in air = 40N
         Readings → 40 – 10.64 = 29.36N
         Or
         40 – 13.33 = 26.67N