Pressure

14 Grade 10 Physics questions on Pressure, with worked marking schemes. 14 questions are available on this topic in full.

1. Question 1

   1 mark

   The hydraulic braking system of a matatu uses oil rather than air in its pipes because liquids

   A. are almost incompressible and so transmit the pressure unchanged

   B. cannot leak out of the brake pipes

   C. are heavier than gases

   D. flow faster through narrow pipes than gases do

   (1 mark)

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2. Question 2

   1 mark

   A school has two open water tanks, one narrow and one wide. Both are filled with water to the same depth. The pressure due to the water at the bottom of the tanks is

   A. greater in the narrow tank because the water there is squeezed together

   B. the same in both tanks

   C. greater in the wide tank because its base is larger

   D. greater in the wide tank because it holds more water

   (1 mark)

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3. Question 3

   4 marks

   Explain why mercury, and not water, is used as the liquid in a simple barometer.

   (4 marks)

   Marking scheme

   Mercury is much denser than water, about 13.6 times as dense (1 mark); therefore a much shorter column of mercury is needed to balance atmospheric pressure, about 0.76 m compared with about 10.3 m of water (1 mark); the instrument can then be made a convenient, portable length (1 mark); in addition mercury does not wet the glass and has a very low vapour pressure, so the vacuum above it stays good and the reading is accurate (1 mark). Total 4 marks.

4. Question 4

   1 mark

   Identical small holes are made all round a plastic bottle at the same level and the bottle is then filled with water. Water spurts out of every hole to the same distance. This observation shows that pressure in a liquid

   A. is the same in all directions at the same depth

   B. becomes greater near a hole than elsewhere

   C. acts only downwards because of the weight of the liquid

   D. depends on the size of the hole

   (1 mark)

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5. Question 5

   3 marks

   A learner of mass 54 kg stands upright on the wooden floor of a classroom. The total area of contact between both shoes and the floor is 0.036 m2. Calculate the pressure that the learner exerts on the floor. (Take g = 10 N/kg)

   (3 marks)

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6. Question 6

   4 marks

   A fish trap is lowered to a depth of 15 m below the surface of Lake Naivasha. Taking the density of the water as 1 000 kg/m3, g as 10 N/kg and atmospheric pressure as 100 000 Pa, determine the total pressure acting on the trap.

   (4 marks)

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7. Question 7

   3 marks

   Account for the fact that atmospheric pressure at the top of Mount Kenya is lower than at Mombasa, and state one effect this has on cooking at that altitude.

   (3 marks)

   Marking scheme

   Atmospheric pressure at a point is caused by the weight of the column of air above that point (1 mark); at the top of the mountain the column of air above is shorter and the air is less dense, so the weight acting on each unit area is smaller (1 mark). Effect: water boils at a temperature below 100 degrees Celsius, so food such as beans or githeri takes much longer to cook (1 mark).

8. Question 8

   1 mark

   The wall of the Masinga dam is built much thicker at the bottom than at the top because

   A. water flows fastest at the bottom of the dam

   B. the water at the bottom is denser than the water at the top

   C. the pressure exerted by the water increases with depth

   D. the whole weight of the water rests on the bottom of the wall

   (1 mark)

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9. Question 9

   1 mark

   Tractors used on the soft, wet soils of a sugar farm in Mumias are fitted with very wide tyres. The wide tyres are used mainly because they

   A. reduce the weight of the tractor acting on the soil

   B. spread the weight of the tractor over a larger area, reducing the pressure on the soil

   C. increase the pressure on the soil so that the tractor grips better

   D. increase the force that the tractor exerts on the soil

   (1 mark)

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10. Question 10

    1 mark

    A rectangular water tank rests on a concrete base. The tank is replaced by another one of the same weight whose base area is half as large. The pressure exerted on the concrete base will

    A. be halved

    B. be doubled

    C. be four times as large

    D. remain the same

    (1 mark)

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11. Question 11

    4 marks

    Describe how a siphon may be used to transfer water from a raised tank to a drum standing on the ground.

    (4 marks)

    Marking scheme

    Fill the tube completely with water so that no air is trapped inside it (1 mark); place one end of the tube below the water surface in the tank and the other end inside the drum (1 mark); the outlet end must be kept lower than the water surface in the tank (1 mark); atmospheric pressure acting on the water surface in the tank pushes water through the tube, and the flow continues until the water level in the tank falls to the level of the tube's inlet or air enters the tube (1 mark). Total 4 marks.

12. Question 12

    1 mark

    A learner takes soda through a straw. The soda rises up the straw because

    A. atmospheric pressure pushes the soda up once the pressure inside the straw is reduced

    B. the vacuum formed in the straw attracts the soda upwards

    C. the learner's suction pulls the soda upwards with a force

    D. the soda is lighter than the air inside the straw

    (1 mark)

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13. Question 13

    5 marks

    In a hydraulic jack used in a garage in Thika, an effort of 120 N is applied to a piston of cross-sectional area 0.0015 m2. The load piston has a cross-sectional area of 0.030 m2.

    (a) Determine the pressure produced in the oil.

    (b) Determine the maximum load that the jack can raise.

    (c) State the principle on which the jack works.

    (5 marks)

    Marking scheme

    (a) Pressure = force / area = $\frac{120}{0.0015}$ (1 mark) = 80 000 Pa (1 mark). (b) Force on load piston = pressure x area = 80 000 x 0.030 (1 mark) = 2 400 N (1 mark). (c) Pascal's principle: pressure applied to an enclosed liquid is transmitted equally to all parts of the liquid (1 mark). Total 5 marks.

14. Question 14

    2 marks

    Define pressure and state its SI unit.

    (2 marks)

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