KCSE 2023 Physics Pressure Revision Questions, Answers

PRESSURE IN SOLIDS

4. Define pressure and state its SI units
5. Ploughing tractors have very wide tyres. Explain why.        (2mk)
6. What is the reason why a trailer carrying heavy loads have many wheels?
7. A student wearing sharp pointed heeled stiletto shoes is likely to damage a soft wooden floor. Explain. (2mk)
8. A block of dimension 2m by 0.1m by 5cm has a mass of 500g and rests on a flat surface. Determine the least pressure that can be exerted by the block on the surface.
9. A box of mass 720kg is placed on a table. If the area of contact in the table is 8m². Calculate the pressure it exerts on the table.
10. A metallic block of mass 50kg exerts a pressure of 10N/m² on the surface.

Determine the area of contact between the block and the surface.    

1. A block measuring 20cm by 10cm by 4cm rests on a flat surface. The block has a weight of 6N. Determine:
2. i) The minimum pressure it exerts on the surface.                       (2 mk)
3.        ii)  The density of the block in kg/m³                                         (3mk)
4. A block of mass 60kg measures 6cm by 5cm by 4cm. Calculate
5. The maximum pressure it can exert.
6. The minimum pressure.

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1. A man of mass 80kg exerts a pressure of 200,000Pa on the ground while standing on both feet.
2. Calculate the area of each foot.                                  
3. How much pressure would be exert if he stands on one foot.
4. a) A woman wearing shoes with sharp pointed heels exerts more pressure than an elephant.  Explain?                                                      (1mks)
5. b) If the weight of the woman is 600N and her heel have an area of 1.0cm² each and the elephant has a weight of 30,500N and each feet has an area of 730cm², Calculate by how much more the woman exerts pressure on the ground than the elephant
6. A pick – up carrying stones weighs 20,000N. The weight is evenly spread across the four tyres. The area of contact of each tire with the ground is 025m². Calculate the pressure exerted by each tire on the ground.
7. A pickup of mass 2000kg has four similar tyres. If the pressure exerted by each tyre on the ground is 500,000N/m², calculate the area of each tyre in contact with the ground.
8. The total weight of a car with passengers is 30,000N. The area of contact of each of the FOUR tyres with the ground is 015m². Determine the minimum car tyre pressure.                                           10cm

60cm

30cm

The figure below shows a box of mass 360kg that measures 60cm by 30cm by 10cm.

   (i) Calculate the Maximum pressure it can exert.            (3mk)

        (ii)  Minimum pressure it can exert.                              (3mk)

15. The figure below shows a block of wood plank of mass 600kg and dimension 5m by 0.2m by 0.3m

0.3m

0.2m

0.5m

Calculate

1. The density of the plank. (3mk)
2. The weight of the plank. (1mk

• The minimum pressure it can exert. (3mk)

PRESSURE IN LIQUIDS

1. Name two factors that affect pressure in fluids. (2mks)

2. State two true facts about pressure in liquids. (2mk)

3. Other than the density and the depth, state any other factor that affects the pressure of a fluid.                                          (1mk)

4. Water is filled in a tall container with holes A, B and C first closed. Indicate on the diagram how the water jets out from the respective holes when the holes are opened. (2mk)

A

B

C 

5. With an appropriate reason, Identify the suitable cross- sectional shape of a dam wall                                                   (2mk)

Water

Water

Wall

(A)

(B)

Wall:……………………………………………………………………………………………

Reason:……………………………………………………………………………………………

6. With an appropriate reason, Identify the suitable cross- sectional shape of a dam wall                                                  2mks)

(A)

(B)

Wall:

……………………………………………………………………………………………

Reason:

……………………………………………………………………………………………

7. Which of the points A and B in the figure below will experience the greatest pressure given that the height of the liquid in the two containers is the same? Explain      (2mk)

h

A

 B

Pressure

 h

Water

Thistle funnel.

The diagram below shows a set up used by a student to show variation of pressure in a liquid.

State and explain the effect on the height, h, when the thistle funnel is moved upwards towards the surface of the liquid.              (2mk)

8. ms are built with thicker walls at the bottom than at the top. Explain why.                                                                                                                                       (2mk)

9. Water tanks in houses are erected as high as possible. Explain. (1 mk)

10. Explain why a hole in a ship near the surface is less dangerous than one near the bottom.

11. A drum which is 2m high contains water to a depth of 5 m and oil of density 0.5g/cm³ extends to the top. Find the pressure exerted at the bottom of drum by the two liquids.

12. The reading of mercury barometer is at 0cm. what is the pressure at the place in N/m². {Assume density of mercury is 1.36 x 10⁴ kg/m³}               (3mk)
13. A submarine is 30m below sea water of density 1g/cm³. if the atmospheric pressure at the place is equivalent to 760mmHg.  Find the total pressure acting on the submarine  (Take density of mercury =13600kg/m³)      (4mk)

14. A submarine is 40m below sea water of density 1020 kg/m³. If the atmospheric pressure at    the place is 103,000Pa, calculate the total pressure acting on the submarine.                                         (4mk)

15. A submarine is 20m below sea water of density 1000 kg/m³. If the atmospheric pressure at    the place is 102,000Pa, calculate the total pressure acting on the submarine.

• A boy is swimming 25m below water level of density 1g/cm³. The atmospheric pressure at this place is equivalent to 72cmHg. Calculate the total pressure on his body in N/m² (take ρ for mercury = 13600kg)

17. A water tank of height 8m is ¾ full. Determine the force exerted on a thin metal plate resting flat at the bottom of the bottom of the tank if the plate has an area of 2cm². The density of water is 1000kg/m³ and the atmospheric pressure =104,000 Pa

19. A water tank of height 6m is Determine the force exerted on a thin metal plate resting flat at the bottom of the bottom of the tank if the plate has an area of 0.5m². Take acceleration due to gravity, g = 10m/s², the density of water to be 1000kg/m³ and the atmospheric pressure P=100,000 Pa          (3mks)
20. The height of mercury column in a barometer is found to be 76cm at a certain place. What would be the height on a water barometer in the same place? (Density of water is 1000kg/m³ and density of mercury is 13600kg/m³).
21. The height of mercury column in a barometer, at a place is 64cm. What would be the height of a column of paraffin in the barometer at the same place? (take density of mercury =13600kgm^-3 and density of paraffin = 800 kg /m³).

21. A hole of diameter 0mm is made in the side of a water pipe. If the pressure of the flow is maintained at 3.0 x 10⁶ Nm^-2, calculate the force with which the water jets out of the hole.               (3mk)

22. A hole of area 200mm² at the bottom of a tank 0m deep is closed with a cork. Determine the force due to water (Density of water is 1000kg/m³, and acceleration due to gravity is 10m/s²

23. The figure below shows a conical flask 15cm high, filled with a liquid of

density 1200kg/m³. The atmospheric pressure of the surrounding is 84,000Pa. determine the pressure at the point marked X at the bottom of the flask.                                                                           (4mk)

Point X

15 cm

24. A cube of side 12cm is completely immersed in a liquid of density 800kgm^-3 so that the top surface of the cube is horizontal and 20cm below the surface of the liquid as shown in the figure below.

20cm

12cm

Calculate the pressure due to the liquid on the cube.

1. i) At a depth of 20cm                                           (2mks)
2. ii) At a depth of 32cm                                           (2mks)

iii)     Hence calculate the force due to the pressure difference between the top

surface and the bottom of the cube                   (3mk)

2.8m

Hole

The figure below shows a cylindrical can filled with a liquid of density 0.8 gcm^-3. A hole of diameter 2.0 cm is drilled at a depth of 2.8 m from the top of the can.

Determine:

 (i)  The cross-sectional area of the hole.                                      (2mks)

(ii)  The maximum pressure exerted by the liquid at the hole.      (2mks)

(iii)  The maximum force exerted on a jet of liquid through the hole. (2mks)

• The figure below shows a tank of height 5m filled with water and oil which are immiscible. Water has a height of 2m and a density of 1000kg/m³ while oil has a height of 3m and a density of 600kg/m³ as shown below. If the atm pressure at the place is 100,000Pa, calculate the total pressure exerted at the base of the tank.

2m

3m

Oil

Water

• The figure below shows a tank of height 7m filled with ethanol and oil which are immiscible. Ethanol has a height of 4m and a density of 8g/cm³ while oil has a density of 0.6g/cm³ as shown below. Calculate the pressure exerted at the base of the tank by the two liquids

4m

Oil

Ethanol

HYDRAULIC MACHINES

1. State the Pascal’s principle.
2. Name two properties of a suitable hydraulic fluid
3. Give a reason why air is not commonly used as the fluid in a hydraulic lift. (1mk)
4. Explain why brakes fail in a hydraulic brake system when air gets in to the system.                                              (2mk)
5. Explain why a liquid and not a gas must be used as the ‘fluid’ in a hydraulic

machine.                                                                    (1mk)

6. The area of larger piston of a hydraulic press is 4m² and that of the other piston is

0.05m². A force of 100m is applied on the smaller piston. How much force is  produced on the larger piston?

7. The areas of the piston of the smaller and larger pistons of a Hydraulic press are 4cm² and 480cm². Calculate the force applied on the smaller piston to raise a load of 8400N on the larger piston.

8. In a hydraulic machine, the pistons of two connected cylinders have radius of 10cm and 100cm A force of 400N is applied on the smaller piston. Calculate the force on the larger piston.
9. Figure shows a hydraulic press system. A force of 200N is applied at the small piston.

Liquid

Area = 180cm²

2

A Bale

   200 N

50 cm²

• State the principle on which the system operates.
• Calculate the weight of the Bale supported by the large piston   (3mks)

10. Figure shows a hydraulic press system. A force of 60N is applied at the

Liquid

Area = 300cm²

2

A Bale

   60 N

10 cm²

small piston. Calculate the weight of the Bale supported by the large piston.                                                                                                              (3mk)

11. The figure below shows a hydraulic brake system of a car_. When a force of 200N is applied on the master cylinder the slave piston experience a force of 8000N. Calculate the area of the master cylinder.

Master piston

Brake pedal

Slave piston

400 cm²

12. The figure below shows two cylinders of different cross-sectional areas

connected with a tube. The cylinders contain an incompressible fluid and

are fitted with pistons of cross-sectional areas 4cm² and 24cm².

Area = 4cm²

P

Area = 24cm²

Q

Incompressible fluid

Opposing forces P and Q are applied to the pistons such that the pistons do not move. If the pressure of the smaller piston is 5 N cm^-2.  Determine force Q.(3mk)

13. The figure below shows a hydraulic brake system of a car. When a force of 400N is applied on the master cylinder the slave piston experience a force of 35,000N. The master piston has an area of 8cm²

Master piston

Brake pedal

Slave piston

Calculate

• The area of the slave piston. (3mk)
• The pressure exerted on the master piston. (3mk)
• Name two reasons why oil is preferred to water as a hydraulic fluid
• State the principle on which the system operates. (1 mk)

                                                                        (2mk)

U-TUBE

1. The U-tube below is filled with water and paraffin as shown. If the density of water is 1g/cm³.

40 cm

  50cm

Water

Paraffin

B

A

        (i)      What can you say about the pressure at point A and B.? (1mk)

        (ii)     Calculate the density of paraffin

2. The figure below show a U-tube filled with two liquids, X and Y. Liquid X has a density of 800Kg/m³ while Y has a density of 1200Kg/m³. Determine the height h of liquid.

h

30 cm

X

Y

3. The U – tube below is filled with two liquids A and B. Liquid B has a density of 6g/cm³. Calculate the density of liquid A.

50cm

20cm

A

B

4. The U – tube below is filled with ethanol and mercury. Ethanol has a density of 8g/cm³. Calculate the density of liquid mercury.

4cm

68 cm

Ethanol

Mercury

Mercury

80cm

h

Oil

Water

The figure below show a U-tube filled with water and oil of densities 1000Kg/m³ and 600Kg/m³ respectively. Determine the height h of liquid.

40 cm

X

Blew here

Mutunga blew in to one end of a U-tube manometer as shown below and the liquid X rose up on the other end by 40cm. If the atmospheric pressure at the place is 103,000 Pa and the density of liquid X is 1200kg/m³, calculate the pressure of his lungs

5. The figure below shows a u – tube containing two liquids L₁ and L₂ of densities 8g/cm³ and 1.8g/cm³ respectively in equilibrium. Given that h₂= 16cm determine h₁                                               (4mk)

L₂

 L₁

h₂

h₁

6. The figure below shows an open-ended manometer connected to a gas supply.

Mercury

Gas supply

  100mm

If the mercury barometer reads 760mm, calculate the pressure of gas in the cylinder (density          of water = 1g/cm³, density of mercury = 13.6g/cm³) (3mks)

7. The figure below shows a water manometer used to measure the pressure of a cooking gas. Calculate the pressure of the gas? (atm pressure = 0 x 10⁵ Pa Density of liquid L = 900g/cm³).                  (3mk)

Gas supply

Liquid L

60cm

8. The figure below shows a mercury manometer of density 13,600kg/m³.

Mercury

Gas supply

  40mm

If the atm pressure is 760mmHg, calculate.

• The pressure of gas in (2mk)
• The pressure of gas in N/m². (3mk)

9. Use the Fig below to answer the questions that follow.

Gas in

Mercury

56mm

A

b

1. i) What pressure is acting on point A?                                                  (1mk)
2. ii) What is the value of pressure difference in the instrument reading.

(1mk)

iii)   If the atmospheric pressure is 760mmHg. What is the value of gas pressure?

(2mks

10. The figure below shows a water manometer used to measure the pressure of a cooking gas. By how much is pressure of the gas above atmosphere pressure? (Density of mercury = 13.6g / cm³). (3mk)

Gas supply

Mercury

60cm

40cm

11. The fig below shows air trapped in a J shaped tube. What is the pressure exerted on the trapped air? ( Density of mercury 13600Kg/m³ atmospheric pressure is 0 x 10⁵ pa) Give your answer in Pascal       (2mks)

Mercury

80cm

Trapped air

13. The figure below shows some air trapped by mercury in a glass tube. The tube is inverted in a dish containing mercury.

Trapped air

Mercury

600 mmHg

Given that the atmospheric pressure is 760 mmHg and the height of mercury column in the tube is 600mm, determine the pressure of the trapped air

• The pressure of the trapped air in
• The pressure of the trapped air in Pascal

12. If the atmospheric pressure is 760mmHg. Calculate the pressure in Pascal’s of the trapped air in the tube shown below. (Density of mercury = 13.6g / cm³).                          (3mk)

Mercury

300mm

60mm

Trapped air

13. The figure below shows an open and closed tube manometer connected at different times, to same gas cylinder. Assuming no loss in pressure from the gas cylinder, calculate the value of h (Take atmospheric pressure =1.0×10⁵Pa , density of mercury =13600kg/m³ and acceleration due to gravity =10N/kg )                                                         (3mks)

20cm

Open manometer

Gas cylinder

Closed manometer

Gas cylinder

h

Vacuum 

14. The figure below shows Hare’s apparatus used for comparing liquid densities.

Suck

Water

30cm

25 cm

Liquid X

Calculate the density of liquid X given that density of water is 1000kgm^-3.(2mk)

Tap

Liquid A

24cm

20 cm

Liquid B

Figure 3 shows the levels of two liquids A and B after some air has been sucked out of the tubes through the tap. If the density of liquid B is 1.2g/cm³  , find the density of liquid A

15. The figure below shows a u – tube containing two liquids L₁ and L₂ of densities 8g/cm³ and 0.5g/cm³ respectively floating on a water surface. If the system is in equilibrium, determine the ratio h₁: h₂                          (3mks)

L₂

L₁

Water

h₂

h₁

HEIGHT OF MOUNTAIN

1. The barometric height in a town is 65cmHg. Given that the standard atmospheric
   pressure is 76cmHg and the density of mercury is 13600kg/m³, determine the altitude of
   the town. (Take density of air = 1.25kg/m³) (3mks
2. A mountain climber with a mercury barometer discovered that the readings of the

barometer at the bottom and top of a certain mountain were 750mmHg and

520mmHg respectively. Given that the density of air between the bottom and top

of the mountain is uniform and equal to 1.25 Kg/m³, estimate the height of the mountain. (Take the density of mercury to be 1.36 x 10⁴ Kg/m³)       (3mk)

3. The height of mercury column in a barometer is found to be 67cm at a certain place. What would be the height on a water barometer in the same place. (Density of water is 1000kg/m³ and density of mercury is 13600kg/m³).                                                                                                    ( 3mk)
4. The height of mercury column in a barometer density 13600kg/ m^-3, at a place is 64cm. What would be the height of a column of paraffin in barometer at the same place. (Density of paraffin = 0 x 10² kg /m³). (3mks)
5. The barometric height at sea level is 76cm of mercury while that at a point on a highland is 74cm of mercury. What is the altitude of the point? Take g = 10m/s², density of mercury = 13600 Kg/m³ and density of air as 25Kg/m³.

(3mk)

ATM PRESSURE

1. Define the term atmospheric pressure and give its SI units (2mk)
2. Explain why it may not be possible to suck a liquid into your mouth using drinking straw on the surface of the moon. (1mk)
3. A barometer was taken from Mount Kenya to Mombasa .Explain the change in mercury level in the barometer. (2mk)
4. A glass is filled with water to the brim and a cardboard placed on top. The glass is then inverted as shown.

Glass

Cardboard

Water

Explain why the cardboard does not fall down.

5. The figure shows a rubber sucker.

Rubber sucker

Smooth surface

Explain why the sucker sticks on a smooth clean surface                        (2mk

6. Explain why a partially inflated balloon released at sea level would become fully inflated at a higher altitude
7. Explain how a drinking straw is used to suck a liquid (3mk)
8. Give a reason why water is not a suitable liquid for use in a barometer (1mk)
9. State one applications of atmospheric pressure. (1mk)
10. Explain why high flying aircraft need to be airtight and have pressurized cabins for people.
11. A tin-can is partially filled with water and heated so that the water boils for some time. Explain what happens to the can when closed tightly and allowed to cool.                                                                                                           (2mks)
12. In an experiment to demonstrate atmospheric pressure, a plastic bottle is partially filled with hot water and the bottle is then tightly corked. After some time the bottle starts to get deformed.

(i)      State the purpose of the hot water.                                              (1mk)

(ii)    State the reason the bottle gets deformed                                   (2mk)

(iii)   Explain your answer in e (ii)                                                        (2mk)

Trapped air

Trapped water

Plastic bottle

AIR

The figure shows an inverted test tube which floats in water enclosed in a plastic bottle.

When the sides of the plastic bottle are squeezed, explain what would be observed.                                                                                          (3 mks)

13. A simple barometer is steadily slanted from vertical position. What happens if there is little air in the space above the mercury?             (1mk)

A

Mercury

760mm

The figure below represents a mercury barometer at sea level..

(i)      What is the name of the part labelled A?                             (1mk)

(ii)     What will happen to the barometric height if the barometer is taken to a place of   higher altitude.?                                                             (1mk)

(iii)    Give a reason for your answer in (ii) above.                               (1mk)

14. Explain why a ball point cover has a small hole
15. The liquid to be transferred has to be at a higher level than the other container where it is being emptied.

16. Three identical tubes containing mercury were inverted as shown.

X

Mercury

760cm

A

B

C

        (i) Indicate on the diagram above the levels of mercury in tube B and C.(1 mk)

        (ii) Explain the effect on the level of mercury in tube A if region X is filled with some air.

17. The figure below shows petrol being siphoned from container (a) to  (b)

(b)

(a)

Tube

Water

State when the liquid will stop flowing through the pipe. Explain your answer.

18. (i) Indicate on the figure below, the direction of flow of the liquid.    (1mk)

A

B

1. ii) Explain what would happen to the flow of the system in the figure above if it was put in a vacuum (2mks)
2. One of the applications of pressure in liquids and gases is the lift pump. The pump is more effective in pumping water if the well is less than 10m at sea level. Explain. (2mks)
3. Explain why;

(i) It is difficult to remove the lid from a preserving jar which was closed when the space above  the food was full of steam                                                      (2 mks)

(ii) A force pump must be used instead of a lift pump to raise water from a deep well over 10m                                             (2 mks)

21. The figure below shows a lift pump used to draw water from a borehole

Storage tank

Water

Piston

Barrel

Valve₂

Valve₁

        (i) Describe briefly how the lift pump works in order to lift water from the borehole

                                                                                 (4mk)

        (ii) State two advantages of a force pump over a lift pump      (2mks)

22. The figure below shows a force pump used to draw water from a borehole

Chamber C

Water

Piston

Barrel

Valve₂

Valve₁

P_a

P_a

        (i) Describe briefly how the force pump works in order to draw water from the borehole   (4mk)

        (ii) State two advantages of a force pump over a lift pump

23. The figure below shows a force pump

  100mm

Piston

Water

Valve V₁

         Explain how the water gets past valve V₂                                        (2mks)

24. The table below shows valves of pressure P in fresh water at different depth.

(i) On the grid provided, plot a graph of pressure (y-axis) against depth (x-axis)        (5mk)

(ii)  Given that the equation    P = P_a + pgh, determine from the graph.

(iii) The value of P_a                                  (1 mk)

                                                                              SCHEEM

25. The figure shows an inverted test tube which floats in water enclosed in a plastic bottle.

Trapped air

Trapped water

Plastic bottle

AIR

When the sides of the plastic bottle are squeezed, explain what would be observed.                                                                                          (3 mks)

ANS Test tube sink ;Pressure is increased on squeezing ; forcing more water into the test tube the weight of the test tube and water exceeds upthrust and sink ;