## Physics Paper 1 Questions and Answers - Mang'u Mock 2020 Exam

PHYSICS
PAPER 1
TIME: 2 HOURS.

Instructions to candidates

• This paper consists of TWO Sections: A and B.
•  ALL working MUST be clearly shown.
• Mathematical tables and electronic calculators may be used.

SECTION A (25 MARKS)

1. The masses of equal volumes of a certain liquid and water was found to be Mand Mw respectively. Given that the density of water is 1/g/cm3 express the density of liquid in terms of Ml and Mw (2mks)
2. Fig 1 shows a screw use to fix pieces of wood. Explain how a metre rule can be used to find the pitch of the screw. (2mks) 3. The figure below shows an object being acted on by two forces F1 and F2 Draw a force F3 that has same effect on the body as the two forces (2mks)
4. The reading on a mercury barometer at a place is 700mm. What will be the pressure in N/M2 if density of mercury is 13600kg/m3 (3mks)
5. Steam pipes are constructed with bond at some point of the pipe State the use of the band
6. State special features in a clinical thermometer and explain how these features makes it measure temperature conveniently (4mks)
7. Two metal rods of same material, same length and same cross-sectional area are used to transfer heat from steam to ice as shown below. Metal A is not lagged but B is lagged. Sketch two graphs in same axis to show how temperatures and .......... between hot end and cold end for the two metals (2mks) 8. What is the reading on vernier calipers shown below. (1mk) 9. The set up above shows a metre rule in equilibrium. Given that the rule is uniform, determine its weight (3mks)
10. A spiral spring of spring constant 20N/M is composed by 10cm. Its released to push a mass of 20g horizontally find the speed at which the mass start moving. (3mks)
11. The figure below shows a graph of velocity against time for a moving body Describe the motion of the body during the 10 seconds (2mks) SECTION B: 55 MARKS

1. Bowman's motion of smoke particles can be studied by using the apparatus show below. 1. Explain the role of the smoke particles, lens and microscope in the experiment (3mks)
2. State and explain what kind of motion is observed within the smoke cell (2mks)
3. State what will be observed if the smoke cell is kept in a very cold environment and the experiment repeated (1mk)
4. Explain briefly why liquids have constant volumes but no constant shapes (2mks)
5. Compare the motion observed on smoke in smoke cell with what would be observed with dust particle suspended in water and viewed with a powerful microscope (2mks)
2.
1. Define the term specific latent heat of vaporization of a substance. (1mk)
2. An immersion heater rated 15W is used to heat a liquid in an open beaker. The beaker contains 300g o liquid. After the liquid boils, the heater is left on for 10 minutes before being switched off. The mass of the liquid is found to have reduced to 296.5g.
1. Determine the heat supplied by heater within the 10 minutes of boiling. (3 mks
2. Determine the specific latent heat of vaporization of the liquid. (3 mks)
3. Explain why this method of determination of latent heat of a substance may not
3.
1. State the archimede's principle. (1 mk)
2. A rectangular block of cross-sectional area of 0.08m2 s immersed in a liquid of density 1200kg/m3. The top and lower surfaces of the block are 20cm and 80 cm below the surface of liquid respectively.
1. Determine the downward force on the top surface of the block. (3 mks)
2. Find the upward force on the lower surface of the block.(3mks)
3. Calculate the upthrust on the block.
3. Explain why bodies in circular motion undergoes acceleration even when the speed is constant (1mk)
4. A particle moving along a circular path of radius 5cm describes an arc of length 2 cm every second. Determine
1. Its angular velocity
2.  Its periodic time (2 mks)
3. Number of evolutions per second (1 mk)
5. A stone of mass 40g is tied to the end of a string 50cm long and whirled in vertical circle at 2 revolutions per second; calculate the maximum tension in the string. (3 mks)
4.
1. A liquid if flowing though a tube of different cross-sectional areas A1, A2 and A3 with velocities V1, V2 and V3 respectively. (2 mks)
2. The figure below shows a Bunsen burner is operation with air hole open 1. Explain how air is drawn into the barrel when the gas supply is opened. (2 mks)
2. State the purpose of metal ring. (1 mk)
3. A pipeline has 15cm diameter to one point and 7.6cm diameter at another point. If the speed of water in the wider section is 1.2m/s. Determine
1. Speed of water in narrow section (3 mks)
2. Rate of discharge (2 mks)
5.
1. Define the term absolute zero temperature (1mk)
2. A mass of a gas was put in a container whose one end was closed with a movable piston. The temperature of the gas was gradually changed while the pressure was held constant. The values of volume at different temperatures were noted. The graph below shows the volume against temperature for the gas. 1. State the law that relates the volume and temperature of the gas as shown on the graph above. (1mk)
2. Given that PV=0.8317 where P is the pressure of the gas, determine the value of P (2mks)
3. A tank contains a gas at pressure of 8 x 105 pa and a temperature of 288K. The gas is heated until its pressure rises to 8 x 10opa. Find the new temperature of the gas given that the volume is constant. (3mks)
4. Using Kinetic theory of matter, explain why, the pressure of a gas rises when volume is reduced (2mks)

MARKING SCHEME

SECTION A (25 MARKS)

1. The masses of equal volumes of a certain liquid and water was found to be Mand Mw respectively. Given that the density of water is 1 g/cm3 express the density of liquid in terms of Ml and Mw (2mks)
• VL = ML
dL
And Vw= Mw    = M  = Mw
d1          dL      L
therefore d2 = ML
Mw
2. Fig 1 shows a screw use to fix pieces of wood. Explain how a metre rule can be used to find the pitch of the screw. (2mks) • Measure the length of the threads part
• Divide length with no. of threads

3. The figure below shows an object being acted on by two forces F1 and F2 Draw a force F3 that has same effect on the body as the two forces (2mks)
• Length = 2.2cm
• Direction and arrow

4. The reading on a mercury barometer at a place is 700mm. What will be the pressure in N/M2 if density of mercury is 13600kg/m3 (3mks)
• P=hdg
=0.7 x13600 x 10
= 95,200

5. Steam pipes are constructed with bond at some point of the pipe State the use of the band
• To provide room for expansion

6. State special features in a clinical thermometer and explain how these features makes it measure temperature conveniently (4mks)
• Scale between 35-42-range within human body temperature,

7. Two metal rods of same material, same length and same cross-sectional area are used to transfer heat from steam to ice as shown below. Metal A is not lagged but B is lagged. Sketch two graphs in same axis to show how temperatures and .......... between hot end and cold end for the two metals (2mks) 8. What is the reading on vernier calipers shown below. (1mk) 0.50
+ 0.05
0.55cm

9. The set up above shows a metre rule in equilibrium. Given that the rule is uniform, determine its weight (3mks)
• Clockwise moment - Anticlockwise moment
0.1w +0.6x1 = 0.4 x 2
W = 0.2 = 2N
0.1

10. A spiral spring of spring constant 20N/M is composed by 10cm. Its released to push a mass of 20g horizontally find the speed at which the mass start moving. (3mks)
• Elastic potential - kinetic energy acquired by mass
Energy in Spring
½ke1 - ½mv2
20x (0.01)2 = 0.02v2

v=  √20 x (0.02)2/0.02
= 0.3162m/s

11. The figure below shows a graph of velocity against time for a moving body Describe the motion of the body during the 10 seconds (2mks) • A body projected vertically upwards at 20m/s reaches the highest point and comes back to the point of projection

SECTION B: 55 MARKS

1. Bowman's motion of smoke particles can be studied by using the apparatus show below. 1. Explain the role of the smoke particles, lens and microscope in the experiment (3mks)
• Smoke particles - reflect light as they move around
• Lens - focuses light into smoke cell
• Microscope - magnifies the smoke particles for easier visibility.

2. State and explain what kind of motion is observed within the smoke cell (2mks)
• Smoke particles are seen moving in a continuous random motion, due to combinement by invisible air molecules

3. State what will be observed if the smoke cell is kept in a very cold environment and the experiment repeated (1mk)
• The random motion of the particles will reduce

4. Explain briefly why liquids have constant volumes but no constant shapes (2mks)
• Intermolecular distance between liquid molecules is constant at a particular temperature hence constant volume.
• The molecules can easily change positions within the bulk of the liquid hence no constant shape

5. Compare the motion observed on smoke in smoke cell with what would be observed with dust particle suspended in water and viewed with a powerful microscope (2mks)
• Higher constant random motion in gone the two weak intermolecular forces.
• Lower constant random motion in liquids due to stronger intermolecular forces.
2.
1. Define the term specific latent heat of vaporization of a substance. (1mk)
• Heat energy required to vapourise a unit mass of a liquid at a constant temperature

2. An immersion heater rated 15W is used to heat a liquid in an open beaker. The beaker contains 300g o liquid. After the liquid boils, the heater is left on for 10 minutes before being switched off. The mass of the liquid is found to have reduced to 296.5g.
1. Determine the heat supplied by heater within the 10 minutes of boiling. (3 mks)
• Heat = power x time
= 15 x 10 x 60
= 9000 Joules

2. Determine the specific latent heat of vaporization of the liquid. (3 mks)
• Heat = Latent heat x mass
9000 = 35      x Lv
1000
Lv = 2.571 x 106J/kg

3. Explain why this method of determination of latent heat of a substance may not
• Some heat is absorbed by containee
• Some heat is radiated away during heating
3.
1. State the archimede's principle. (1 mk)
• An object partially or fully submerged in a liquid experiences upthrust equal to weight displaced.

2. A rectangular block of cross-sectional area of 0.08m2 s immersed in a liquid of density 1200kg/m3. The top and lower surfaces of the block are 20cm and 80 cm below the surface of liquid respectively.
1. Determine the downward force on the top surface of the block. (3 mks)
• F = PxA
= 0.2 x 1200 x 10 x 0.008
= 192N

2. Find the upward force on the lower surface of the block.(3mks)
3. Calculate the upthrust on the block.
3. Explain why bodies in circular motion undergoes acceleration even when the speed is constant (1mk)
• Bodies moves in constantly changing directions hence acceleration.

4. A particle moving along a circular path of radius 5cm describes an arc of length 2 cm every second. Determine
1. Its angular velocity
• W = θ/t
θ1= arc length = 2 = 0.4

=0.4/1

2.  Its periodic time (2 mks)
• f =  w    =   0.4   = 0.0637sec
2Π       6.284
T = 1/f
=15.71sec

3. Number of evolutions per second (1 mk)
• no of revolutions/sec=f=0.0637

5. A stone of mass 40g is tied to the end of a string 50cm long and whirled in vertical circle at 2 revolutions per second; calculate the maximum tension in the string. (3 mks)
• T = mv2 + mg
r
V=2Jrf = 6.284m/s
= 0.04 x 39.4889 +0.4
0.5
= 3.159N
4.
1. A liquid if flowing though a tube of different cross-sectional areas A1, A2 and A3 with velocities V1, V2 and V3 respectively. (2 mks)
• V1   1   = VA = K
A1
V2   1   = V2A2 = K
A2
V1A1 = V2A2

2. The figure below shows a Bunsen burner is operation with air hole open 1. Explain how air is drawn into the barrel when the gas supply is opened. (2 mks)
• Air enters the barrel at very high speed creating low pressure within barrel, air of forced in the barrel by atmospheric pressure to occupy the low pressure region

2. State the purpose of metal ring. (1 mk)
• To regulate the amount of air entering

3. A pipeline has 15cm diameter to one point and 7.6cm diameter at another point. If the speed of water in the wider section is 1.2m/s. Determine
1. Speed of water in narrow section (3 mks)
• A1V1 = A2V2
0.0176 x 1.2 = 4.536 x V2
Therefore V2 = 4.655m/s

2. Rate of discharge (2 mks)
• volume flux = AV = 0.0211m3/s

5.
1. Define the term absolute zero temperature (1mk)
• Temperature at which gases molecules ceases to move

2. A mass of a gas was put in a container whose one end was closed with a movable piston. The temperature of the gas was gradually changed while the pressure was held constant. The values of volume at different temperatures were noted. The graph below shows the volume against  temperature for the gas. 1. State the law that relates the volume and temperature of the gas as shown on the graph above. (1mk)
• Charles law - That temperature of a fixed mass of a gas is directly proportional to absolute temperature as long as p is constant.

2. Given that PV=0.8317 where P is the pressure of the gas, determine the value of P (2mks)
• Slope =   (5 - 1.8)    x 10-3
600 - 200

8 x 10-6m3/K = 0.831
OP

= P = 103Pa

3. A tank contains a gas at pressure of 8 x 105 pa and a temperature of 288K. The gas is heated until its pressure rises to 8 x 10opa. Find the new temperature of the gas given that the volume is constant. (3mks)
• P1 = P2
T1    T2
= 8 x 105
288
= 8 x 106
T2
T2 - 2880Pa

4. Using Kinetic theory of matter, explain why, the pressure of a gas rises when volume is reduced (2mks)
• Number of collisions increases due to decreased volume bence increased pressure.

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