Sec 3 Physics Pressure topical questions

Calculate the pressure in each case.

1. (a)A 90 N force spreads over an area of 0.30 m².[2]
2. (b)The same force concentrated on 0.0030 m².[2]

A glass marble has mass 5.2 g and volume 2.0 cm³.

1. (a)Calculate the density of the glass in g/cm³.[2]
2. (b)Express this density in kg/m³.[1]

A pond is 1.5 m deep. Take the water’s density as 1000 kg/m³ and g = 10 N/kg.

1. (a)Calculate the pressure due to the water at the bottom.[2]
2. (b)State one direction in which this pressure acts at a point on the pond floor.[1]

A teacher of weight 640 N stands on a platform of three legs, each of contact area 25 cm².

1. (a)Calculate the total contact area in m².[1]
2. (b)Calculate the pressure exerted on the floor.[2]
3. (c)One leg sinks slightly into soft vinyl. Explain why in terms of pressure.[2]
4. (d)State one change to the platform design that would prevent the sinking.[1]

A workshop hydraulic press has a small piston of area 4.0 cm² and a large piston of area 300 cm². A worker leans on the small piston with 150 N.

1. (a)Calculate the pressure in the liquid.[2]
2. (b)Calculate the output force on the large piston.[2]
3. (c)The worker’s piston descends 6.0 cm. Calculate how far the large piston rises.[2]
4. (d)State the energy assumption behind your answer to (c).[1]

A bottle of water stands on a table. Two holes are opened, one 8.0 cm and one 32 cm below the water surface. Take ρ = 1000 kg/m³, g = 10 N/kg.

1. (a)Calculate the water pressure at each hole.[2]
2. (b)How many times larger is the lower pressure? Compare with the ratio of the depths.[2]
3. (c)State what happens to both jets as the water level falls.[2]

A manometer uses oil of density 900 kg/m³. Connected to a gas pipe, its liquid levels differ by 5.0 cm. Take g = 10 N/kg.

1. (a)Calculate the excess pressure of the gas above atmospheric.[2]
2. (b)Atmospheric pressure is 101 000 Pa. Calculate the absolute gas pressure.[1]
3. (c)The manometer is refilled with mercury of density 13 600 kg/m³. Calculate the new height difference, in mm.[2]

A hydraulic car lift raises a 1200 kg car. The large piston has area 0.080 m²; the small piston, area 0.00050 m². Take g = 10 N/kg.

1. (a)Calculate the weight of the car and the minimum pressure the liquid must supply.[3]
2. (b)Calculate the force needed on the small piston.[2]
3. (c)The car rises 25 cm. Calculate the work done on the car and the distance the small piston must travel if the applied force is 750 N.[3]

A tall water tank feeds a tap through a pipe. The water surface in the tank stands 12 m above the tap. Take ρ = 1000 kg/m³, g = 10 N/kg, atmospheric pressure 100 kPa.

1. (a)Calculate the pressure due to the water at the tap.[2]
2. (b)Explain why the water flows even though the atmospheric pressure acts on both the tank surface and any leak at the tap.[2]
3. (c)A sealed, air-tight tank cannot let air in as water leaves. State and explain what happens to the flow.[3]

A weather balloon of volume 12 m³ is filled with helium at ground level where atmospheric pressure is 100 kPa. It rises to a height where the pressure is 50 kPa. The balloon skin is elastic and the temperature is constant.

1. (a)Estimate the balloon’s volume at the higher altitude, using the pressure ratio.[3]
2. (b)Explain the volume change in terms of pressure balance.[2]
3. (c)State what eventually limits the balloon’s ascent.[2]

A student argues: "A 2-tonne elephant exerts more pressure on the ground than a 50 kg woman in stiletto heels, because the elephant weighs more." Assess the claim with calculations. Elephant: four circular feet, each 0.020 m². Stiletto heel: one heel of area 1.0 × 10⁻⁴ m² bearing the woman’s full weight on each step; take g = 10 N/kg.

1. (a)Calculate the elephant’s pressure on the ground.[3]
2. (b)Calculate the woman’s pressure through one heel.[3]
3. (c)Assess the student’s claim.[2]

A simple barometer is made with a long tube of oil (density 920 kg/m³) inverted over a dish of the same oil. Atmospheric pressure is 101 kPa. Take g = 10 N/kg.

1. (a)Calculate the height of the oil column that atmospheric pressure can support.[2]
2. (b)The tube is only 9.0 m long. State and explain what is observed.[2]
3. (c)A drop in atmospheric pressure to 98 kPa occurs. Calculate the change in the column height.[3]