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.
 The figure below shows the scale of a measuring instrument when measuring the thickness of an object.
Figure 1 Name the instrument to which the scale belongs. (1 mark)
 Find the reading of the instrument shown. (2 marks)
 A solid weighs 32.5N on the surface of the moon. The force of gravity on the moon is 1.7Nkg1. Determine the mass of the solid. (3 marks)
 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)
 Briefly explain why rooms are at a lower level and ventilators at a higher level. (2 marks)
 State the Archimedes principle. (1 mark)
 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  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)
 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)
 The efficiency of a pulley system is always less than 100%. State two reasons. (2 marks)
 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)  How much current is taken by a bulb whose rate is 100 and which is designed for mains supply of 240V? (3 marks)
 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.

 Define centripetal acceleration. (1 mark)
 Distinguish between angular and linear velocity. (2 marks)
 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; Position A. (3 marks)
 Position B. (3 marks)
 At what point is the string likely to cut. Explain. (2 marks)

 Explain why it is advisable to use the pressure cooker for cooking at high altitudes. (2 marks)
 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;
 The heat absorbed by the water. (2 marks)
 Heat absorbed by the electric kettle. (2 marks)
 The time taken for the water to boil . (2 marks)
 How much longer it will take to boil away all the water? (3 marks)

 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)
 The figure below shows a force distance graph for a car being towed on a level ground.
 Calculate the total work done. (2 marks)
 If the velocity just before reaching C is 0.6 m/s. Calculate the power developed by the engine at this point. (2 marks)

 State the pressure law; (1 mark)
 Explain how a gas exerts pressure. (2 marks)
 The figure below shows a set up used to verify pressure law.
 State the measurement that may be taken in the experiment. (2 marks)
 Explain how the measurement in (i) above may be used to verify pressure law. (2 marks)
 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)

 State the law of conservation of energy. (1 mark)
 The diagram below shows a pulley system, a mass of 10kg is raised 2m by an effort of 80N.
 Calculate the distance moved by effort. (2 marks)
 How much potential energy does the load gain? (1 mark)
 How much work is done by the effort? (1 mark)
 What is the efficiency of these pulleys? (2marks)
 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)
 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/m3while the density of the liquid was 800kg/m3. Determine the;
 Volume of the liquid displaced. (2marks)
 Upthrust on the stone. (4marks)
 Reading on the spring balance.
MARKING SCHEME
SECTION A (25 MARKS)
Answer ALL the questions in this section in the spaces provided.
 The figure below shows the scale of a measuring instrument when measuring the thickness of an object.
Figure 1 Name the instrument to which the scale belongs. (1 mark)
 Vernier calliper
 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
 Main scale 5.00
 Name the instrument to which the scale belongs. (1 mark)
 A solid weighs 32.5N on the surface of the moon. The force of gravity on the moon is 1.7Nkg1. Determine the mass of the solid. (3 marks)
 M = ^{w}/_{g}
= ^{32.5}/_{1.7}
= 19.117 kg / 19.12 kg
 M = ^{w}/_{g}
 A mercury barometer reads 760mmHg at sealevel and 700mmHg at the top of a mountain. If the density of mercury is 13,600kg/m^{3} and average density of air is 1.30kg/m^{3}, 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
 Difference in pressure 760 – 700 = 60mm
 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.
 Warm air being lighter raises and escapes through the ventilators while the colder air gets in through the windows and doors.
 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.
 When a body is partially or totally immersed in a fluid, it experiences an upthrust equal to the weight of the fluid displaced.
 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
 Wood being a poor conductor of heat does not allow the excess heat so it gets charred
 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
 Air space is to allow for expansion of water when it freezes preventing the glass bottle from breaking
 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.
 Frictional force is equal to the applied force but in opposite direction. The net applied force is zero.
 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.
 Friction between moving parts of the pulley system / friction.
 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.
 The hot metal rod breaks the surface tension of the water; surface behaving like stretched skin is pulled towards Y.
 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
 P = IV
 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
 P.E = ^{Fe}/_{2}
SECTION B (55 MARKS)
Answer ALL the questions in this section in the spaces below.

 Define centripetal acceleration. (1 mark)
 This is a force that maintains a body in circular motion and directed towards the centre
 This is a force that maintains a body in circular motion and directed towards the centre
 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.
 Angular velocity is rate of change of angular displacement with time while linear velocity is rate of change of linear displacement with time.
 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; Position A. (3 marks)
 T = MV^{2}/rmg
= (0.2 × 5^{2}/0.5) (0.2 ×10)
= 10 – 2 = 8N
 T = MV^{2}/rmg
 Position B. (3 marks)
 T = MV^{2}/r
= (^{(0.2 × 25)}/_{0.5})
T = 10N
 T = MV^{2}/r
 At what point is the string likely to cut. Explain. (2 marks)
 At C, because tension is high at 12N
T = ^{MV2}/_{r}+mg
 At C, because tension is high at 12N
 Position A. (3 marks)
 Define centripetal acceleration. (1 mark)

 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
 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
 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;
 The heat absorbed by the water. (2 marks)
 Q = MCΔθ
= 3kg x 4200JKg^{1}k^{1} x 80
= 240 x 4200 = 1008000J / 1.008kJ
 Q = MCΔθ
 Heat absorbed by the electric kettle. (2 marks)
 Q = M_{k}C_{k}Δθ
= 450 x 80 = 36000J
 Q = M_{k}C_{k}Δθ
 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
 pt = total heat absorbed
 How much longer it will take to boil away all the water? (3 marks)
 pt = mLv
3000t = 3 x 2.3 x 10^{6}
t = (3 ×2.3 × 10^{6})/3000
t = 2300 seconds
 pt = mLv
 The heat absorbed by the water. (2 marks)
 Explain why it is advisable to use the pressure cooker for cooking at high altitudes. (2 marks)

 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)
 v^{2} = u^{2} + 2as
O^{2} = 900^{2} + 2 x a x 0.10
900 = 0.20 a
a = ^{(900)}/_{0.20}
a = 450 m/s^{2} (negative a must)
 v^{2} = u^{2} + 2as
 The figure below shows a force distance graph for a car being towed on a level ground.
 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
 Total work done = Area under graph
 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
 P = force x velocity
 Calculate the total work done. (2 marks)
 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)

 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.
 The pressure of a fixed mass of gas is directly proportional to absolute temperature provided that volume is kept constant.
 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
 When a gas is heated it expands increasing the number of collusions per unit area which in turn raise the pressure
 The figure below shows a set up used to verify pressure law.
 State the measurement that may be taken in the experiment. (2 marks)
 Temperature of water
 Pressure gauge reading
 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
 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
P_{1}/T_{1} = P_{2}/T_{2}
^{500000}/_{300}= P_{2}/348
P2 = ^{(500000 ×348)}/_{300}
= 580000
P2 = 5.8 x 105 Pa
 P α T →P=KT →K=P/T
 State the measurement that may be taken in the experiment. (2 marks)
 State the pressure law; (1 mark)

 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
 The sum of kinetic energy and potential energy of a system is constant
 The diagram below shows a pulley system, a mass of 10kg is raised 2m by an effort of 80N.
 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
 V.R = 2 =^{ (Distance moved by load)}/_{(Distance moved by effort)}
 How much potential energy does the load gain? (1 mark)
 P.E = mgh
= 10 x 10 x 2
= 200J
 P.E = mgh
 How much work is done by the effort? (1 mark)
 Work input = Effort x Effort distance
= 80N x 1m
= 80 Joules
 Work input = Effort x Effort distance
 What is the efficiency of these pulleys? (2marks)
 MA/VR x 100% = efficiency
(^{100}/_{80})/2 x 100% =^{ 5000}/_{80}
Eff = 62.5%
 MA/VR x 100% = efficiency
 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
 With long handle spanner the effort used is less than short handle spanner so one does a lot of work
 Calculate the distance moved by effort. (2 marks)
 State the law of conservation of energy. (1 mark)
 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^{3}while the density of the liquid was 800kg/m^{3}. Determine the;
 Volume of the liquid displaced. (2marks)
 V = ^{4}/_{3000}
V = 1.33 x 103m^{3} (At least 2 d.p)
 V = ^{4}/_{3000}
 Upthrust on the stone. (4marks)
 Upthrust = Weight of liquid displaced = vρg
Liquid; 800 x 1.33 x 10^{3} x 10
= 10.64 N
Upthrust in water = v
1.33 x 103m^{3} x 10 x 1000
= 13.33N
 Upthrust = Weight of liquid displaced = vρg
 Reading on the spring balance.
 Weight of stone in air = 40N
Readings → 40 – 10.64 = 29.36N
Or
40 – 13.33 = 26.67N
 Weight of stone in air = 40N
 Volume of the liquid displaced. (2marks)
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