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

PHYSICS
PAPER 1
(THEORY)
FORM 4 TERM 1 OPENER EXAMS
TIME: 2 HOURS

INSTRUCTIONS TO CANDIDATES

• Answer all the questions in the spaces provided.
• Mathematical tables and electronic calculators may be used.
• All workings must be clearly shown where necessary.

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

1. Figure below shows part of a micrometer screw gauge. Use the information and the figure to answer questions 1 and 2.
   
   State the pitch of the micrometer screw gauge. (1mk)
2. State one limitation of the micrometer screw gauge. (1mk)
3. A lorry of weight 20000N is brought to rest on a uniform bridge, by applying brakes, as shown in the figure below. The weight of the bridge is 60000N and is 20m long. It is supported at P and Q. calculate the reactions at P and Q. (3mks)
   
4. The ticker-time tape below shows a section of a long tape. The dots were made at a frequency of 40Hz.
   
   Determine the acceleration of the trolley pulling the tape 3mks.
5. State and explain any changes observed in a Brownian motion, when the temperature of the air in the smoke cell is increased. (2mks)
6. A wooden block of mass 2kg is placed on a horizontal surface. A horizontal force of 14N is exerted on it which makes it to accelerate at 5ms-1.
   Find the frictional force acting between the surfaces. (3mks)
7. Sketch a velocity time graph for a body thrown vertically upwards to a maximum height. (1mk)
   
8. Lycopodium is lightly sprinkled on a clean water surface in a large tray. A red hot needle is plunged into the centre of the water surface. State and explain the observation made. (2mks)
9. A tight rope walker carries a pole to maintain stability. Explain how he uses it to achieve it. (1mk)
10. Figure below shows two set-ups by a student using identical lamps and thermometers.
    
    In which set up is thermometer reading a higher temperature, if the lamps are switched on for some duration? Explain (2mks)
11. The system in the figure below is a set-up which can be used to illustrate expansion of liquids.
    
    State one way of modifying the apparatus so that the rise in level for a particular temperature is higher. (1mk)
12. A heavy log lying on the ground requires more energy to start moving than the same log which is already in motion. Explain why. (1mk)
13. State the reason why the speed of water at a wider section of a river is lower than at a narrower section. (1mk)
14. A hole is made at the middle of a tall jar container and water is poured into it to the level shown. See figure below.
    
    1. Explain why water comes out of the hole, yet the atmosphere pressure acting in the directions shown are equal in magnitude. (2mks)
    2. What would be observed if the container was filled with water and the top lid closed tightly? (1mk)

SECTION B (55 MARKS)

15. A circuit consists of a battery, a metal wire, an ammeter and a switch connected in series. The switch is closed and the ammeter reading noted. The metal wire is now heated.
    1. State the observation made on the ammeter reading and give a reason for your answer (2mks)
    2. State the purpose of a fuse in a circuit. (1mk)
    3. An electric heater is made of wire of resistance 100Ω and 2400 V mains supply. Determine
       1. Power rating of the heater (3mks)
       2. Current flowing in the circuit (3mks)
16.  
    1. The figure below shows a pulley system.
       
       1. What is the velocity ratio of the system? (1mk)
       2. Calculate the efficiency of the system. (3mks)
       3. Give one reason why efficiency is not 100%. (1mk)
    2. Light helical spring obeying Hooke’s Law was attached to a fixed support. When a 5N load was hung on it, the length of the spring was 160mm. when a 10N load was hung on it the length became 200mm. determine
       1. The length of the spring with no load. (3mks)
       2. The length of the spring with 8N. (3mks)
17.    
    1. Sketch a vernier callipers scale reading 3.89cm. (2 marks)
    2. In an experiment to estimate the diameter of an oil molecule, an oil drop of diameter 0.05cm spread over a circular patch whose diameter is 20cm.
       Determine:
       1. The volume of the oil drop. (2 marks)
       2. The area of the patch covered by the oil. (2 marks)
       3. The diameter of oil molecule. (3 marks)
       4. State one assumption made in (b) above. (1 mark)
       5. Three possible sources of error in this experiment. (2 marks)
18. The speed of a train, hauled by a locomotive varies as shown below as it travels between two stations along a straight horizontal track.
    
    
    Use the graph to determine
    1. The maximum speed of the train. (1 mark)
    2. The acceleration of the train during the first 2 minutes of the journey. (2 marks)
    3. The time during which the train is slowing down. (2 marks)
    4. The total distance in metres between the two stations. (4 marks)
    5. The average speed in m/s of the train. (3 marks)
19.    
    1. Explain how a person is able to draw milk from a glass using a straw. (2mks)
    2. The following diagram shows a simplified hydraulic breaking system of a car.
       
       
       1. State the property of the liquid (oil) that makes it more suitable for use as a brake fluid than a gas. (1mk)
       2. Explain how the system works, starting from when the driver presses the foot pedal. (4mks)
       3. Why would the system not function properly if air leaked into the cylinder? (1mk)
    3. A hydraulic jack has a piston (large piston) diameter of 0.32m while its plunger (small piston)has a diameter of 0.052m. A force of 500N is exerted on the plunger. Determine the upward force in the large piston. (3mks)

MARKING SCHEME

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

1. Figure below shows part of a micrometer screw gauge. Use the information and the figure to answer questions 1 and 2.
   
   State the pitch of the micrometer screw gauge. (1mk)
   0.5mm
   
2. State one limitation of the micrometer screw gauge. (1mk)
   Cannot measure internal diameters
   
3. A lorry of weight 20000N is brought to rest on a uniform bridge, by applying brakes, as shown in the figure below. The weight of the bridge is 60000N and is 20m long. It is supported at P and Q. calculate the reactions at P and Q. (3mks)
      
   Taking moments about to end Q
   60,000 x 10 + 20,000 x 14 = Tp x 20
   Tp = 44,000N
   But T_Q+Tp = 60,000 + 20,000
   T_Q= 80,000 - 44,000 = 36,000
   
   
4. The ticker-time tape below shows a section of a long tape. The dots were made at a frequency of 40Hz.
   
   Determine the acceleration of the trolley pulling the tape 3mks.
   u=^4.5/_0.025 = 180cm/s, v = ^0.3/_0.025 = 12m/s
   a= v-u
          t
   =    12-180  
        6 x 0.025
   
   
5. State and explain any changes observed in a Brownian motion, when the temperature of the air in the smoke cell is increased. (2mks)
   Increase Brownian motion because of higher kinetic energy of air molecules that cause increased collisions
   
6. A wooden block of mass 2kg is placed on a horizontal surface. A horizontal force of 14N is exerted on it which makes it to accelerate at 5ms^-1.
   Find the frictional force acting between the surfaces. (3mks)
   F=ma
   F= 2x5 = 10N
   Fr= Force applied - resultant force - Formula can be implied substitution
   = 14-10
   =4N
   
   
7. Sketch a velocity time graph for a body thrown vertically upwards to a maximum height. (1mk)
   
   Check for straight line intercepts(initial velocity & final velocity)
   Negative acceleration.
   
   
8. Lycopodium is lightly sprinkled on a clean water surface in a large tray. A red hot needle is plunged into the centre of the water surface. State and explain the observation made. (2mks)
   A clear circle is formed
   Surface tension is broken at the centre hence no force in the middle
   
   
9. A tight rope walker carries a pole to maintain stability. Explain how he uses it to achieve it. (1mk)
   Turns the pole around to maintain the COG vertically above the point.
   
10. Figure below shows two set-ups by a student using identical lamps and thermometers.
    
    In which set up is thermometer reading a higher temperature, if the lamps are switched on for some duration? Explain (2mks)
    Convectional current takes place
    
11. The system in the figure below is a set-up which can be used to illustrate expansion of liquids.
    
    State one way of modifying the apparatus so that the rise in level for a particular temperature is higher. (1mk)
    Make the bore of capillary tube narrower
    
12. A heavy log lying on the ground requires more energy to start moving than the same log which is already in motion. Explain why. (1mk)
    More energy is required to overcome static frictional force than dynamic/ kinetic frictional force
    Static frictional forces are greater/larger/ bigger than Dynamic/Kinetic frictional forces
    
    
13. State the reason why the speed of water at a wider section of a river is lower than at a narrower section. (1mk)
    Volume flux is constant
    
14. A hole is made at the middle of a tall jar container and water is poured into it to the level shown. See figure below.
    
    1. Explain why water comes out of the hole, yet the atmosphere pressure acting in the directions shown are equal in magnitude. (2mks)
       The sum of atmospheric pressure and pressure of the water acting downwards is more than only atmospheric pressure acting horizontally, the pressure difference pushes the water through the hole
       
    2. What would be observed if the container was filled with water and the top lid closed tightly? (1mk)
       No water will flow out, there will be no pressure to balance the horizontal pressure difference.

SECTION B (55 MARKS)

15. A circuit consists of a battery, a metal wire, an ammeter and a switch connected in series. The switch is closed and the ammeter reading noted. The metal wire is now heated.
    1. State the observation made on the ammeter reading and give a reason for your answer (2mks)
       The ammeter reading decreases. The resistance of the metals decreases with increase in temperature.
       
    2. State the purpose of a fuse in a circuit. (1mk)
       A fuse open/breaks an electric circuit when current flow exceeds certain amount. 
       
       
    3. An electric heater is made of wire of resistance 100Ω and 2400 V mains supply. Determine
       1. Power rating of the heater (3mks)
          P= v2/R = 2402/100=     576W               
          
       2. Current flowing in the circuit (3mks)
          I= p/v = ⁵⁷⁶/₂₄₀
16.  
    1. The figure below shows a pulley system.
       
       1. What is the velocity ratio of the system? (1mk)
          VR=3
          
       2. Calculate the efficiency of the system. (3mks)
          N=^MA/_VR x 100
          400/150 x 100%
                   3
          = 88.88%
       3. Give one reason why efficiency is not 100%. (1mk)
          Friction between the movable parts of the pulley.
          Work is done in lifting the movable parts of the pulley system.
          
          
    2. Light helical spring obeying Hooke’s Law was attached to a fixed support. When a 5N load was hung on it, the length of the spring was 160mm. when a 10N load was hung on it the length became 200mm. determine
       1. The length of the spring with no load. (3mks)
          F=ke
          5= K(0.160 – l_o)
          10 = K(0.2 – l_o)
          The formula may be implied.
          ⁵/₁₀=0.16l_o/0.02l_o
          1.5 l_o = 1.6 - 10 l_o
          (10 – 5) l_o = 1.6 – 1
          5 l_o = 0.6
          l_o = 0.12m
          = 12cm
       2. The length of the spring with 8N. (3mks)
          F= Ke
          10 = K X 0.08
          K = ¹⁰/_0.08=¹⁰⁰⁰/₈=125N/m        
          E= f/k    =8/125 x 100 =6.4cm
          L = L_o + e
          = 12+ 6.4 = 18.4cm
          
          
17.    
    1. Sketch a vernier callipers scale reading 3.89cm. (2 marks)
       
    2. In an experiment to estimate the diameter of an oil molecule, an oil drop of diameter 0.05cm spread over a circular patch whose diameter is 20cm.
       Determine:
       1. The volume of the oil drop. (2 marks)
          Volume = 4/3Πr^{3
          4}/₃ x ²²/₇ x 0.025³ 
          =6.548 x 10^-5 cm³
          
       2. The area of the patch covered by the oil. (2 marks)
          ²²/₇ x 10²
          =314cm²
       3. The diameter of oil molecule. (3 marks)
          Area x diameter of the molecule = vol
          Diameter of the molecule= 
          6.548 x 10^-5
                314
          =20.09 x 10^-7cm
          
       4. State one assumption made in (b) above. (1 mark)
          Oil drop is spherical
          Oil patch is a monolayer
          
       5. Three possible sources of error in this experiment. (2 marks)
          Getting right oil
          Measuring drop diameter
          Measuring diameter of the oil patch
          Getting a drop of the right size
          
          
18. The speed of a train, hauled by a locomotive varies as shown below as it travels between two stations along a straight horizontal track.
    
    Use the graph to determine
    1. The maximum speed of the train. (1 mark)
       22.5m/s
       
       
    2. The acceleration of the train during the first 2 minutes of the journey. (2 marks)
       V = u + at
       22.5 = 0 + 120a
       22.5 = 120a
       0.1875m/s = a
       
       
    3. The time during which the train is slowing down. (2 marks)
       =3min
       =3 x 60
       =180sec
       
       
    4. The total distance in metres between the two stations. (4 marks)
       = ½ (a + b) h
       = ½ (300 + 600) 22.5
       = ½ ((5x60))22.5
       = 10,125m
       
       
    5. The average speed in m/s of the train. (3 marks)
       average speed= ^{total distance}/_{total time}
       ¹⁰⁸⁰⁰/_10x60
       18m/s
       
       
19.    
    1. Explain how a person is able to draw milk from a glass using a straw. (2mks)
       When one sucks from the straw, the pressure inside the straw is reduced
       This allows the atmospheric pressure on surface of milk up the straw and to the mouth
       
       
    2. The following diagram shows a simplified hydraulic breaking system of a car.
       
       
       1. State the property of the liquid (oil) that makes it more suitable for use as a brake fluid than a gas. (1mk)
          Oil is incompressible
          
          
       2. Explain how the system works, starting from when the driver presses the foot pedal. (4mks)
          When driver steps on the foot peddle, the force is transmitted through the lever system to the piston in the master cylinder.
          The pressure produced in the master cylinder is transmitted through the fluid to the wheel (or slave) cylinder where the pistons are pushed out. The piston inturn push the break shoe outwards.
          This makes the brake lining to press the rotating wheel causing the car to slow down or to stop.
          
          
       3. Why would the system not function properly if air leaked into the cylinder? (1mk)
          Air is compressible and so the force exerted would be partially used to compress the air instead of pushing out the brake shoe.
          
          
    3. A hydraulic jack has a piston (large piston) diameter of 0.32m while its plunger (small piston)has a diameter of 0.052m. A force of 500N is exerted on the plunger. Determine the upward force in the large piston. (3mks)
       d= 0.32m
       f= ?
       f= 500
       d= 0.052m
       ^f1/_A1=^F2/_A2√(1)

       F2= ^F1/_A1 X A2

       =      500      X π X 0.16²
          π X 0.026²  

       = 18935 N √1