PHYSICS
PAPER 1
FORM 4 MID TERM 2
INSTRUCTIONS
 This Paper has Section A nd B. Answer all questions in Section A nd B
 Working must be clearly shown.
SECTION A (25 marks)
Answer all the questions in this section in the spaces provided
 Figure 1 below shows a part of Vernier calipers used to determine the length of a metallic cube. If the cube has a mass of 1533g.
Determine the density of the cubein g/cm^{3} (3marks)  Figure 2 below shows a mercury manometer. Some dry gas is trapped in one of the limbs.
Given that the atmospheric pressure is 76cm of mercury. Determine the pressure of the gas in mmHg (3 marks)  When it is raining, it is advisable not to touch a canvas tent from inside. Explain. (1 mark)
 State the reason why it is easier to separate water into drop than to separate a piece of solid into smaller pieces. (1 mark)
 Figure 3 below shows a simple fire alarm.
Explain how it works (2marks)  It feels hotter to sit on a metallic chair that has been left in the sun for a long time than wooden bench at the same temperature. Explain(2 marks)
 State the principle of moments. (1 Mark)
 A uniform meter rule of mass 10g is balanced by masses 24 g and 16g suspended at 0 cm mark and 100cm mark respectively. Determine the position of the pivot. (2 marks)
 The figure below shows a compression spring, before and after a mass of 5kg was placed on it. Use it to answer questions 9, 10, and 11.
Find the spring constant of the spring. (3marks)  Sketch a graph of force against length if different masses were used in the above set up. (1 mark)
 Explain the shape of the graph above (1 mark)
 State Bernoulli’s effect (1 mark)

 Water flows through a pipe of different crosssection areas as shown in the diagram below. Indicate in the diagram the levels of water in tubes A, B and C. (1 mark)
 Give a reason for your answer in 13(a) above. (1 mark)
 Water flows through a pipe of different crosssection areas as shown in the diagram below. Indicate in the diagram the levels of water in tubes A, B and C. (1 mark)

 An electric heater is placed at equal distances from two similar metal cans A and B filled with water at room temperature. The outer surface of can A is shiny while that of can B is dull black. State with reasons which can will be at a higher temperature after the heater is switched on for some time. (2marks)
 Sketch a graph of temperature against time for can A and B after the heater is switched off. (1 mark)
SECTION B: (55 marks)

 State Charles’ law. (1 mark)
 The Set up below was used to verify Charles’ law. Use it to answer the following questions.
 State two measurements taken from the above set up. (2marks)
 Describe briefly how the set up above can be used to verify Charles’s law. (3marks)
 State the function of sulphuric acid index. (1 mark)
 Pressure of the trapped air remains unchanged throughout the experiment. Explain how this is possible. (2marks)
 A mass of 1200 cm^{3} of oxygen at 270 C and a pressure 1.2 atmosphere is compressed until its volume is 600 cm3 and its pressure is 3.0 atmospheres. Find the temperature of the gas after compression (2 marks)

 Define the term heat capacity. (1 mark).
 In experiment to determine the specific latent heat of vaporization Lv of water, steam was passed into cold water in a copper calorimeter. The following data was obtained:
Mass of calorimeter 105.2g
Mass of calorimeter + water =228.8 g
Mass of calorimeter + water + steam= 231.2g
Temperature of the cold water = 180C
Final temperature of the water=290 C Determine the amount of steam that condensed. (1 mark)
 Calculate the amount of heat lost by the condensed steam. (specific heat capacity of water=4200J/Kg/K) (3 marks)
 Calculate the amount of heat absorbed by water and the calorimeter (specific heat capacity of copper = 390J/kg/K) (3marks)
 Calculate the specific latent heat of vaporization Lv of water. (2 marks)
 Explain why cooling the water used in the calorimeter to below room temperature could have led to more accurate result. (1 mark)

 Distinguish between elastic collision and inelastic collision. (1 mark)
 A van of mass 1500 kg travelling at a constant velocity of 72 km/h collides with a stationary car of mass 900kg. The impact takes 2 seconds before they move together at a constant velocity for 20 seconds. Calculate:
 Their common velocity (3marks)
 The distance moved after the impact.(2marks)
 The impulsive force (3marks)
 The change in kinetic energy (3marks)
 Why is the kinetic energy not conserved in this collision (1 mark)

 Define angular velocity. (1 mark).
 Figure 4 below shows a mass 500g moving in vertical circle having a radius of 35cm at a constant velocity. It makes 2 revolutions in one second.
 Indicate on the diagram the direction of centripetal force. (1 mark)
 Calculate the linear velocity of the mass. (3marks)
 Calculate the centripetal acceleration of the object. (2marks)
 Determine the centripetal force. (3marks)
 Giving a reason, state the point at which the string is likely to snap. (2mark)

 State the law of conservation of energy. (1 mark)
 Figures4 below shows a ball of mass of 5kg rolling along a frictionless path as shown.
 Calculate the potential energy of the ball at point O. (2 marks)
 Determine the velocity of the ball at point A (2 marks)
 If the ball rolls back when it reaches point B, state the energy changes that takes place O to B. (1 mark)
 It is observed that the efficiency of the machine increases when it is used to lift large loads. Give a reason for this (1 mark)
MARKING SCHEME
 Length= 5.35cm
Volume= 5.35 x 5.35 x 5.35 = 28.6225cm3
p= m/v = 1533/28.6225 = 53.5593g/cm3  Total pressure = atm + ρgh
= 760mmHg+20mmHg
= 780mmHg  This breaks the surface tension of water running over the canvas tent hence increasing adhesive force so that the tent leaks.
 Cohesive forces are stronger in solids than in liquids

 In case of fire outbreak, the temperature increases, brass expands more than iron.
 The bimetallic strip bends towards the iron side and makes the contact.
 This completes the circuit causing the electric bell to ring.
 The metallic chair is a good conductor of heat and gains heat faster than the wooden bench, which is a poor conductor of heat
 For a system in equilibrium, the sum of clockwise moments is equal to the sum of anticlockwise moments
 (xx24) = (100x)16+(x50)10
24x=1600  16x+10x500
24x=11006x
x=36.67cm  F=ke
50=k x 0.2
K= 500/2 = 250N/M
K=250 n/m 
 The length of the spring reduces as the masses are added until it cannot reduce anymore
 For a fluid that is nonviscous incompressible and the flow is streamline, then an increase in velocity causes a corresponding decrease in pressure it exerts.


 Water level in manometer B is lower than the levels in manometer A and C. Water level in manometer A is the highest hence high pressure compared to B and C.


 B will have a higher temperature than the water in A. Dull surfaces are good obsorbers of heat


 For a fixed mass of gas volume is directly propotional to absolute temperature provided pressure is kept constant.


 Length of the air column trapped / volume of air (L)
 Temperature of the water bath

 Temperature is varied and corresponding value of L and T are recorded
 A grapgh of L vs absolute temperature T is then plotted
 Straight line is obtained cutting the xaxis at OK(273ºC)

 Sulphuric acid index acts as a pointer in the volume of the gas on the scale
 Pressure of the trapped air is the same as the atmospheric pressure pluse pressure due to acid index which remains constant through the experiment
 Vi=1200cm^{3} , T=27+273=3000K
p=1.2atm
p1V1 = p2v2 → 1.2 x 1200 = 3 x 600
T_{1} T_{2} 300 t_{2}T_{2} → 375K or 102ºC


 A quantity of heat required to change the temperature of a given mass of a substance by 1Kelvin

 231.2228.8=2.4g
 Steam condensed to water at 29ºC
Steam 100ºC → water 100ºC → Water 29ºC
Q=MLV+MCO
=(0.003 x lv+894.6)  Heat absorbed = mc cc o + mw cw o
=0.105 x 390 x (2918)+0.1236x x 42.0x(2918)
=480.45+5710 32
=6190.77j  Heat lost  heat gained
0.003Lv + 894.6=6190.77
0.003Lv=Ω96.17
Lv= 1,765390 0r 1.765 x 10^{6} j/kg  This balances the heat exchange between the calorimeter with its contents and the surrounding.


 Elastic collision both momentum and kinetic energy of colliding bodies is conserved
 Inelastic collision only momentum is conserved but not kinetic energy
 Moment before collision = momentum after collision
 (1500 x 20)+0=2400 x v
12.5m/s=v  s=ut=12.5m/s x 0=250m
 ft=mv mu
fx2=1500(2012.5)
fx2=11250→f= 5625
or ft=mvmu
fx2=900x12.5
f5625N  Initial KE=^{1}/_{2} mu^{2}
=^{1}/_{2 }x 1000x 20^{2}= 300,000
Final KE=^{1}/_{2}(m_{1}m_{2})v^{2}
=^{1}/_{2 }x 2400 x 12.52=187,500J
KE change= 300000187500= 112500J  This is the energy converted to sound and heat or energy used in doing work
 (1500 x 20)+0=2400 x v


 Rate of change of angular displacement


 f=2Hz
ω= 2πf
= 2 x 3.142x2
= 12.56
V= r ω
= 0.35 x 12.56
= 4.3982m/s  a=v^{2}/r=(4.3982)^{2}
0.35
=55.270m/s^{2}  f=mv^{2}/r=0.5 x 55.270
=27.635N  At point R. This is where tension is maximum in the string


 The sum of kinetic energy and potential energy of a system is constant
 PE=mgh=5x10x20=1000J
 PE=KE
mgh=^{1}/_{2} mv^{2}
v^{2}=2gh
v^{2}=2x10x20
v^{2}=400
v=20m/s  PE →KE → PE + heat energy + sound
 Efficiency increase because as the load increases energy used in overcoming frictionand lifitng the weight of the machine parts becomes insignificant.
 MA advatage increase because friction and weight of the machine parts remain constant.

 The sum of kinetic energy and potential energy of a system is constant
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