pressure MCQs for UPSC Prelims

25 practice questions on pressure from the Pressure, Winds, Storms, and Cyclones section of the UPSC Prelims syllabus. 25 come with a written explanation. Try the sample set below - the answer stays hidden until you ask for it.

8 Easy 12 Medium 5 Hard

Sample questions

Q1
easy

Pressure is best described as

  1. A the weight of an object
  2. B the area on which a force acts
  3. C the force acting on each unit of area
  4. D the total force acting on an object
Show answer and explanation

Correct answer: C - the force acting on each unit of area

Pressure tells us how much force is shared by each unit of area, which is why the same force can give very different pressures. The total force by itself says nothing about how it is spread. Area alone is not a force, and weight is only one particular force that can cause pressure.

Q2
hard

A box weighing $120\ \text{N}$ can be stood either on a face of area $2\ \text{m}^2$ or on a face of area $6\ \text{m}^2$. The difference between the two pressures it exerts is

  1. A $20\ \text{N/m}^2$
  2. B $40\ \text{N/m}^2$
  3. C $60\ \text{N/m}^2$
  4. D $80\ \text{N/m}^2$
Show answer and explanation

Correct answer: B - $40\ \text{N/m}^2$

On the smaller face the pressure is $120 \div 2 = 60\ \text{N/m}^2$, and on the larger face it is $120 \div 6 = 20\ \text{N/m}^2$. The difference is $60 - 20 = 40\ \text{N/m}^2$. The values $60$ and $20\ \text{N/m}^2$ are the two separate pressures rather than their difference, and $80\ \text{N/m}^2$ comes from adding them.

Q3
hard

A tractor meant for soft, wet fields is fitted with very wide tyres, while a racing bicycle runs on thin tyres. The best explanation is that

  1. A the width of a tyre has no effect on pressure
  2. B wide tyres lower the pressure on soft ground so that the tractor does not sink in
  3. C thin tyres lower the pressure on the road
  4. D wide tyres raise the pressure on the ground so that the tractor grips better
Show answer and explanation

Correct answer: B - wide tyres lower the pressure on soft ground so that the tractor does not sink in

Wide tyres share the tractor's weight over a large patch of soil, so the pressure stays low and the wheels stay on the surface instead of digging in. Thin tyres press the same weight into a narrow strip, which raises the pressure rather than lowering it. Since pressure depends on the area of contact, tyre width matters a great deal.

Q4
hard

Two nails of the same metal are hammered with equal force into the same plank. One has a sharp tip and the other has a slightly flattened tip. Which goes in further, and why?

  1. A Both go in equally, because the hammer force is the same
  2. B The flattened one, because it is heavier
  3. C The flattened one, because a larger area gives a greater pressure
  4. D The sharp one, because the same force acts over a smaller area and gives a greater pressure
Show answer and explanation

Correct answer: D - The sharp one, because the same force acts over a smaller area and gives a greater pressure

With the force fixed, the nail with the smaller tip area produces the greater pressure and drives deeper into the wood. A larger area always lowers the pressure, so the flattened nail does worse. Equal force does not mean equal pressure, and the tiny difference in weight of the tips is not what matters.

Q5
medium

A nail is made with a pointed tip and a broad flat head. The pointed tip is there

  1. A to reduce the pressure on the wood
  2. B to make the nail easier to see in the plank
  3. C to make the nail lighter to carry
  4. D to create a very large pressure on the wood so that the nail goes in
Show answer and explanation

Correct answer: D - to create a very large pressure on the wood so that the nail goes in

The tip touches the wood over an extremely small area, so the hammer blow becomes a huge pressure and the wood gives way. Reducing the pressure would make the nail harder to drive in. The shape of the tip has almost no effect on the weight of the nail, and being easy to see is not a scientific reason.

Q6
medium

A tall bottle full of water has small holes punched in its side at different heights. Water spurts out farthest from

  1. A the lowest hole
  2. B the middle hole
  3. C all the holes equally
  4. D the highest hole
Show answer and explanation

Correct answer: A - the lowest hole

The pressure of a liquid grows with depth, so the water at the lowest hole is pushed out hardest and travels farthest. Water at the top hole has little depth above it and dribbles out. Since the depths differ, the jets cannot be equal.

Q7
medium

A girl of weight $400\ \text{N}$ stands on both feet, and her shoes cover a total area of $0.04\ \text{m}^2$. The pressure she exerts on the floor is

  1. A $1000\ \text{N/m}^2$
  2. B $10000\ \text{N/m}^2$
  3. C $16\ \text{N/m}^2$
  4. D $100\ \text{N/m}^2$
Show answer and explanation

Correct answer: B - $10000\ \text{N/m}^2$

Dividing the weight by the area gives $400 \div 0.04 = 10000\ \text{N/m}^2$. Multiplying the two numbers gives $16\ \text{N/m}^2$, which reverses the rule. The values $100$ and $1000\ \text{N/m}^2$ come from misplacing the decimal point while dividing by $0.04$.

Q8
easy

Which of these is designed to spread a force over a large area?

  1. A The tip of a syringe needle
  2. B The tip of a drawing pin
  3. C The wide track of a bulldozer
  4. D The cutting edge of an axe
Show answer and explanation

Correct answer: C - The wide track of a bulldozer

A bulldozer runs on wide tracks so that its great weight is spread out and the machine does not sink into soft ground. A drawing pin, an axe edge and a needle tip are all made small on purpose, so that a modest force gives a very high pressure and pierces or cuts.

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