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

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

1. 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]
2. 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]
3. State the SI unit of density [1 mk]
4. Give a reason why heat transfer by radiation is faster than heat transfer by conduction [1 mk]
5. 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]
6. State the principle of moments [1 mk]
7. 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]
8. 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]
9. State the three factors on which the rate of heat flow depends on. [3 mks]
10. 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.
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]
2. 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]
3.
1. You are provided with the following:-
• A block of wood
• A spring balance
• 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]
4.
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

1. 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

2. 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

3. State the SI unit of density [1 mk]
• Kilograms per cubic metre
4. 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.
5. 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

6. 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.

7. 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

8. 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/gt2
54.2 = 0 +1/g x 1.082
g= 92.94m/s2

9. 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

10. 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.
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.

2. 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 Fa [3 mks]
• Fa/0.01 = 700/0.2
• Fa = 35N
Fo x 1 = Fa x 0.2
Fo = 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
3.
1. You are provided with the following:-
• A block of wood
• A spring balance
• 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-3
Determine:
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
4.
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
2. The tension on the string at position A [3 mks]
• TA = mrw2 = mg
• 0.1 x 0.4 x 12.5682 - 0.1 x 10
• TA = 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

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