Physics Questions and Answers - Form 3 Mid Term 2 Exams 2023

QUESTIONS

1.  
   1. Define surface tension?(1mk)
   2. The diagram below shows drop of liquids X and Y carefully put on a clean flat glass slab
      
      Explain the shapes of the drops (2mks)
2. An empty density bottle has a mass of 50g. Its mass is 100g when filled with water and 120g when filled with liquid K. Calculate the density of liquid K in SI units. (3mks)
3. A block measuring 20cm by 10cm by 4cm rests on a flat surface. The block has a weight of 6N. Determine:
   1. The minimum pressure it exerts on the surface. (2mks)
   2. The maximum pressure it exerts (2mks)
   3. The barometric height of a certain town is 65cmHg. Given that the standard atmospheric pressure is 76cmHg and the density of mercury is 13600kg/m³, determine the altitude of the town. (Take density of air = 1.25kg/m³ (3mks)
4.  
   1. The figure below shows a uniform metal rod balanced at the centre by different forces.
      
      Determine the value of T. (3mk)
   2. Explain why a lorry loaded with bags of maize packed high up is likely topple over when negotiating a corner. (2mks)
5. Figure below shows a tape made from a ticker tape timer running at 50Hz.
   
   Find,
   1. The time taken for one tick interval (1mk)
   2. Velocities between points AB and DE (3mk)
   3. Acceleration of the body over interval AE (2mk)
6.  
   1. Distinguish between reflection and refraction of light (1mk)
   2. State the two laws of refraction of light(2mk)
   3. The refractive indices of water and glass are 4/3 and 3/2 respectively. Determine the refractive index of a ray of light moving from water to glass. (3mks)
   4. A ray of light makes a glancing angle of incidence i = 60° with a flat glass surface as shown in figure
      
      Given that the critical angle for glass is 42° determine;
      1. The refractive index of glass (2mks)
      2. The angle of refraction r (2mks)
      3. Given that the speed of light in air 3.0 x 10⁸ m/s, find the speed of light in glass (2mks)
   5. The graph shown below shows, the apparent depth (y-axis) against real depth. Use it to calculate the refractive index of glass. (3mks)
      
7.  
   1. Define the term inertia (1mk)
   2. The figure below shows a smooth card placed on the open end of a car. A coin is placed on the card. When the card is horizontally pulled away suddenly, the coin drops in the can.
      
      Explain this observation.(2mks)
   3. A car of mass 800 kg is initially moving at 25m/s. Calculate the force needed to bring the car to rest over a distance of 20m.(3mks)
   4. A bullet of mass 0.006kg is fired from a gun of mass 0.5kg. If the muzzle velocity of the bullet is 300m/s. calculate the recoil velocity of the gun.( 3mks)
8. State two forms of energy (2mks)

MARKING SCHEME

1.  
   1. Define  surface tension?(1mk)
      • is a force that makes the surface of a liquid to behave like a thin elastic stretched skin.
   2. The diagram below shows drop of liquids X and Y carefully put on a clean flat glass slab                             
      Explain the shapes of the drops     (2mks)
      • In x adhesive forces are stronger than the cohesive forces while in y, the cohesive forces are stronger than the adhesive forces.
2. An empty density bottle has a mass of 50g. Its mass is 100g when filled with water and 120g when filled with liquid K. Calculate the density of liquid K in SI units. (3mks)
   Mass of water = 100 − 50 = 50g         
   Mass of liquid k = 120 − 50 = 70g
   volume_{water  =} ⁵⁰/₁ ,= 50cm³     
   But, density =  mass   = ⁷⁰/₅₀ =1.4g/cm³
                          volume
3. A block measuring 20cm by 10cm by 4cm rests on a flat surface. The block has a weight of 6N. Determine:
   1. The minimum pressure it exerts on the surface. (2mks)
      p = ^F/_A, ⁶/_0.02 = 300N/M² 
   2. The maximum pressure it exerts(2mks)
      p = ^F/_A, ⁶/_0.004 = 1500N/M²
   3. The barometric height of a certain town is 65cmHg. Given that the standard atmospheric pressure is 76cmHg and the density of mercury is 13600kg/m³ , determine the altitude of the town. (Take density of air = 1.25kg/m³ (3mks)
      (hpg) air =(hpg)mercury
      h = 0.11×13600×10 = 1196.8m
                1.25 × 10
4.  
   1. The figure below shows a uniform metal rod balanced at the centre by different forces.
      Determine the value of T.
      S.C.M = S.A.M                   T =¹⁸⁰/₅₀ = 3.6N
      (4 x 35) + 50T = 8 x 40
      14 + 50T = 320
      50T=180                              (3mks)
   2. Explain why a lorry loaded with bags of maize packed high up is likely topple over when negotiating a corner.(2mks)
      • Packing maize high up raises the c.o.g making the lorry unstable.
5. Figure below shows a tape made from a ticker tape timer running at 50Hz.
   Find,
   1. The time taken for one tick interval
      T = ¹/_F = ¹/₅₀ = 0.02s
   2. Velocities between points AB and DE
      v_AB = ⁵/_0.02 = 250cm/s
      v_DE = ¹⁵/_0.02 = 750cm/s
   3. Acceleration of the body over interval AE
      a = v − u, 750−250 = 8333.3cm/s² 
               t       3×0.02
6.  
   1. Distinguish between reflection and refraction of light (1mk)
      • Reflection refers to the bouncing of light when it strikes bright surface while refraction refers to the bending of light at the interface as it travels from one medium to another.
   2. State the two laws of refraction of light(2mk)
      Sin i/sin r = n (Snell’s law)
      Normal ray, incident ray and refracted ray all lie on the same plane
   3. The refractive indices of water and glass are 4/3 and 3/2 respectively. Determine the refractive index of a ray of light moving from water to glass.
      21n = ⁿ²/_n1 = ³/₂ × ¾ = ⁹/₈ 
   4. A ray of light makes a glancing angle of incidence i = 60° with a flat glass surface as shown in figure
      Given that the critical angle for glass is 42° determine;
      1. The refractive index of glass (2mks)
         n =   1    =     1    = 1.494
              sinC     sin42
      2. The angle of refraction r (2mks)
         sinr = sin60  , r = 35.43
                   1.494
      3. Given that the speed of light in air 3.0 x 10⁸ m/s, find the speed of light in glass (2mks)
         Vg = 3.0x10⁸ = 200,803,212.8m/s
                   1.494
   5. The graph shown below shows, the apparent depth (y-axis) against real depth.  Use it to calculate the refractive index of glass. (3mks)
      g = Δy = 20
            Δx     40
      But n =¹/_g = 2
7.  
   1. Define the term inertia
      • Tendency of a body to remain in its state of rest or in uniform motion unless acted upon by an external force.        (1mk)
   2. The figure below shows a smooth card placed on the open end of a car. A coin is placed on the card. When the card is horizontally pulled away suddenly, the coin drops in the can.
      Explain this observation.(2mks)
      • This is because the can tends to remain in its state of rest.
   3. A car of mass 800 kg is initially moving at 25 m/s.  Calculate the force needed to bring the car to rest over a distance of 20 m.(3mks)
      v = u + 2as                                  F = ma = 800 x 15.625 = 12500N
      0 = 625 +2 x a x 20
      ^40a/₄₀ = ⁶²⁵/₄₀    
      a = ⁶²⁵/₄₀ = 15.625m/s²
   4. A bullet of mass 0.006kg is fired from a gun of mass 0.5kg. If the muzzle velocity of the bullet is 300m/s. calculate the recoil velocity of the gun.( 3mks)
      m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂
      (0.006x0) + (0.056x0) = (0.006x300) + 0.5xv₂   
      V = −3.6m/s
8. State two forms of energy (2mks)
   • Chemical energy
   • Mechanical energy