Physics Paper 1 Questions and Answers - Sukellemo Joint Mock 2020/2021

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SUKELLEMO JOINT MOCK
Kenya Certificate of Secondary Education
PHYSICS PAPER 1
2 hours

Instructions to Candidates

Answer all the questions in the spaces provided.
This paper consists of 2 sections: Section A and B
All working must be clearly shown.
Non-programmable silent electronic calculators and KNEC mathematical tables may be used.

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

The level of water in a burette is at 30 cm³. 400 drops of water each of volume 0.015 cm³ was removed from the burette.
Determine the new level of water in the burette [3 mks]
Calculate the temperature change of water as it falls through a height of 20 m. (Take g = 10 N/kg and s.h.c of water =4200 J/kg/K) [3 mks]
State the SI unit of density [1 mk]
Give a reason why heat transfer by radiation is faster than heat transfer by conduction [1 mk]
A railway truck of mass 4000 kg moving at 3 m/s collides with a stationary truck of mass 2000 kg. The couplings join and the trucks move off together. Calculate their common velocity after collision. [3 mks]
State the principle of moments [1 mk]
An air bubble with a volume of 1 cm³ escapes from the helmet of a diver at a depth of 200 m below the water surface. What will be the volume of the bubble immediately it breaks the surface of water? (Take atmospheric pressure = 10 m of water) [4 mks]
Calculate the acceleration due to gravity on a planet where an object released from rest falls through a height of 54.2 m in 1.08 s. [3 mks]
State the three factors on which the rate of heat flow depends on. [3 mks]
Under a driving force of 3000 N, a car of mass 1200 kg has an acceleration of 1.3 m/s². Find the frictional resistance acting in the car. [3 mks]

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

1. Explain the following as regards the solar heater:
  1. Why the pipe is fixed to a dark-coloured collector plate. [1 mk]
  2. Why the pipe is made of copper [1 mk]
  3. Why the pipe is coiled several times [1 mk]
  4. Why the collector plate is fixed to an insulator. [1 mk]
  5. Why the panel front is covered with glass. [1 mk]
2. Liquids expand when heated and contract when cooled. However this is not always true for water.
  1. What name is given to the behavior of water? [1 mk]
  2. States two importance of this behavior of water. [2 mks]
  3. State any two disadvantages of this behavior. [2 mk]
  4. A man wants to fit a brass ring onto a steel rod of diameter equal to the inner diameter of the ring. Explain how this can be achieved [2 mk]
The figure below shows a hydraulic press supporting a load F.
1. What properties of liquids make them suitable for use in hydraulic machines such as the one above? [2 mks]
2. If A and a are areas of cross-section of the pistons, and the lengths of the arm are as given, find:
  1. The force Fo [3 mks]
  2. The mechanical advantage [1 mks]
  3. The efficiency of the machine [3 mks]
  4. State two reasons why the efficiency of a pulley system is always less than 100% [2 mks]
1. You are provided with the following:-
  - A block of wood
  - A spring balance
  - Thin thread
  - Overflow can
  - A small measuring cylinder
  - Some liquid
    
    With the aid of a labeled diagram an experiment to the law of floatation
2. The diagram below shows a car acid hydrometer.
  1. Indicate on the diagram above the minimum and the maximum measurement to be taken. [2 mks]
  2. State the reason why the bulb is wide. [2 mks]
3. 1. Figure below shows a uniform plank of weight 20N and length 1.0m balanced by a 0.5kg mass at a distance x from the pivot point O.
    
    Determine the value of X [2 mks]
  2. When the block is completely immersed in water the pivot O must shift by 0.05 m to the left for the system to balance. The density of water is 1000 kgm-3.Determine:
    1. The upthrust U on the block. [3 mks]
    2. The volume of the block. [2 mks]
1. 1. Distinguish between elastic and inelastic collisions. [2 mks]
  2. A body of mass 5 kg is ejected vertically to a height of 7.2 m from the ground when a force acts on it for 0.1s. Calculate the force used to eject the body.[3mks]
2. Explain why the moon is said to be accelerating when revolving around the earth at constant speed [2mks]
3. A stone is whirled in a vertical circle as shown in the figure below using a string of length 40 cm. A, B, C and D are various positions of the stone in its motion. The stone makes 2 revolutions per second and has a mass of 100g.
  1. Calculate:
    1. The angular velocity [ 3mks]
    2. The tension on the string at position A [3 mks]
  2. At C where the stone has acquired a constant angular speed, the string cuts. The stone takes 0.5 seconds to land on the ground. How high is point C above the ground. [2 mks]
  3. How far does it travel horizontally before hitting the ground. [2 mks]

MARKING SCHEME

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

The level of water in a burette is at 30 cm³. 400 drops of water each of volume 0.015 cm³ was removed from the burette.
- Volume of drops =(400 x 0.015)cm³ = 6cm³
  Determine the new level of water in the burette [3 mks]
- New level = (30+6)=36cm³
Calculate the temperature change of water as it falls through a height of 20 m. (Take g = 10 N/kg and s.h.c of water =4200 J/kg/K) [3 mks]
- G.P.E = Heat again
  Mwgh = MwCwΔθ
  10 x 20 = 4200Δθ
  Temperature change Δθ = 0.0476ºC
State the SI unit of density [1 mk]
- Kilograms per cubic metre
Give a reason why heat transfer by radiation is faster than heat transfer by conduction [1 mk]
- Radiation is propagated by means of e.m waves while conduction involves movement of particles which are prone to distraction through collisions.
A railway truck of mass 4000 kg moving at 3 m/s collides with a stationary truck of mass 2000 kg. The couplings join and the trucks move off together. Calculate their common velocity after collision. [3 mks]
- m₁u₁ + m₂u₂ =(m₁ + m₂)
  4000 x 3 + 0= 6000v
  v= 2m/s
State the principle of moments [1 mk]
- Sum of clockwise moments about a point is equal to the sum of anticlockwise moments about the same point.
An air bubble with a volume of 1 cm³ escapes from the helmet of a diver at a depth of 200 m below the water surface. What will be the volume of the bubble immediately it breaks the surface of water? (Take atmospheric pressure = 10 m of water) [4 mks]
- P₁V₁ = P₂V₂
  P₁ = (200 +10)m
  V₁ = 1cm³
  P₂ = 10m
  v₂ = ?
  210m x 1cm³ = 10m x V₂
  v₂ = ²¹⁰/₁₀
  =21cm³
Calculate the acceleration due to gravity on a planet where an object released from rest falls through a height of 54.2 m in 1.08 s. [3 mks]
- s= ut + ¹/₂gt²
  54.2 = 0 +¹/₂g x 1.08²
  g= 92.94m/s²
State the three factors on which the rate of heat flow depends on. [3 mks]
- Length of the conductor
- The cross section area of the conductor
- The material of the conductor
- Temperature difference of the ends of a conductor
Under a driving force of 3000 N, a car of mass 1200 kg has an acceleration of 1.3 m/s². Find the frictional resistance acting in the car. [3 mks]
- F=ma
  1200 x 1.3
  F= 1560N
  F = 3000 -1560
  1440N

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

1. Explain the following as regards the solar heater:
  1. Why the pipe is fixed to a dark-coloured collector plate. [1 mk]
    - To get heated faster since dark is a good absorber and emitter
  2. Why the pipe is made of copper [1 mk]
    - To conduct heat needed for heating water.
  3. Why the pipe is coiled several times [1 mk]
    - To increase the surface area for heating
  4. Why the collector plate is fixed to an insulator. [1 mk]
    - To minimize heat losses to the environment
  5. Why the panel front is covered with glass. [1 mk]
    - To prevent escape of the reflected radiant heat which has a longer wavelength
2. Liquids expand when heated and contract when cooled. However this is not always true for water.
  1. What name is given to the behavior of water? [1 mk]
    - Anomolous expansion of water.
  2. States two importance of this behavior of water. [2 mks]
    - Enables the survival of aquatic during winters
    - Enables weathering of rocks to take place.
  3. State any two disadvantages of this behavior. [2 mk]
    - Can cause accidents in water transportation
    - Can cause pipe bursts
  4. A man wants to fit a brass ring onto a steel rod of diameter equal to the inner diameter of the ring. Explain how this can be achieved [2 mk]
    - Heat the ring to allow its diameter increase. Fix the rod into the hole and allow the two to cool.
The figure below shows a hydraulic press supporting a load F.
1. What properties of liquids make them suitable for use in hydraulic machines such as the one above? [2 mks]
  - Incompressible
  - Non-errosive
2. If A and a are areas of cross-section of the pistons, and the lengths of the arm are as given, find:
  1. The force F_a [3 mks]
    - ^Fa/_0.01 = ⁷⁰⁰/_0.2
    - F_a = 35N
      F_o x 1 = F_a x 0.2
      F_o = 35 x 0.2
      =7N
  2. The mechanical advantage [1 mks]
    - M.A = ^L/_E
    - ⁷⁰⁰/₇
    - M.A = 100
  3. The efficiency of the machine [3 mks]
    - VR = V.Rl x VRh
      ^0.2/_0.01 x ¹/_0.2
      V.R = 100
    - ^M.A/_V.R x 100%
    - ¹⁰⁰/₁₀₀ x 100%
  4. State two reasons why the efficiency of a pulley system is always less than 100% [2 mks]
    - Part of the applied effort is raising the blocks
    - Some energy is overcoming friction between the moveable parts
1. You are provided with the following:-
  - A block of wood
  - A spring balance
  - Thin thread
  - Overflow can
  - A small measuring cylinder
  - Some liquid
    With the aid of a labeled diagram an experiment to the law of floatation
  - Measure the weight of blocks of wood in air
  - Fill the overflow can with the liquid and let the excess liquid flow out then place an empty measuring cylinder below the spout
  - Place the block of wood in the overflow can and measure the volume of the displaced liquid inside the cylinder
  - Using the density of the liquid, calculate the mass and then weight of the displaced liquid
  - Compare the weight of the block with the value of the weight of the displaced liquid
2. The diagram below shows a car acid hydrometer.
  1. Indicate on the diagram above the minimum and the maximum measurement to be taken. [2 mks]
    - Q- minimum
    - P- maximum
  2. State the reason why the bulb is wide. [2 mks]
    - To displace the large volume of liquid to provide sufficient upthrust necessary for floating.
3. 1. Figure below shows a uniform plank of weight 20N and length 1.0m balanced by a 0.5kg mass at a distance x from the pivot point O.
    
    Determine the value of X [2 mks]
    - 20(0.5 -x) = 5x
      x = 0.4m
  2. When the block is completely immersed in water the pivot O must shift by 0.05 m to the left for the system to balance. The density of water is 1000 kgm^-3Determine:
    1. The upthrust U on the block. [3 mks]
      - F x 0.45= 20 x 0.05
        F = 2.222
      - U = 5 - 2.222
        U = 2.778N
    2. The volume of the block. [2 mks]
      - U = pVg
        1000 x 10 x v = 2.778
        V= 2.778 x 10^-4m³
1. 1. Distinguish between elastic and inelastic collisions. [2 mks]
    - For elastic collision, both K.E and momentum are conserved while for inelastic collision only momentum is conserved.
  2. A body of mass 5 kg is ejected vertically to a height of 7.2 m from the ground when a force acts on it for 0.1s. Calculate the force used to eject the body.[3mks]
    - v² = u² - 2gs
      0= u² - 2 x 10 x 7.2
      u= 12m/s
      v=0
    - Ft = momentum
      F= ^{5 x 12}/_0.1
      =600N
2. Explain why the moon is said to be accelerating when revolving around the earth at constant speed [2mks]
  - Because instantenous change in velocity in terms of direction
3. A stone is whirled in a vertical circle as shown in the figure below using a string of length 40 cm. A, B, C and D are various positions of the stone in its motion. The stone makes 2 revolutions per second and has a mass of 100g.
  1. Calculate:
    1. The angular velocity [ 3mks]
      - w = 2πf
      - 2 x 3.142 x 2
      - 12.568 rads^-1
    2. The tension on the string at position A [3 mks]
      - T_A = mrw² = mg
      - 0.1 x 0.4 x 12.568² - 0.1 x 10
      - T_A = 5.318N
  2. At C where the stone has acquired a constant angular speed, the string cuts. The stone takes 0.5 seconds to land on the ground. How high is point C above the ground. [2 mks]
    - h = 1/2gt²
      0.5 x 10 x 0.5²
      h= 1.25m
  3. How far does it travel horizontally before hitting the ground. [2 mks]
    - v=wr
      12.568 x 0.4
      5.027m/s
    - R = ut
      5.027 x 0.5
      2.514m