Force And Pressure

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Q1. A force of 10 N is applied on an area of 2 m². What is the pressure exerted?
Pressure = Force / Area. Here, Force = 10 N and Area = 2 m². So, Pressure = 10/2 = 5 Pa. The unit of pressure is Pascal (Pa). 20 Pa would be force × area, 10 Pa would be force only, and 0.2 Pa would be area / force. So 5 Pa is correct.

Q2. Which statement best explains why a camel can walk easily on sand?
Camels have wide, padded feet that spread their weight over a large area. This reduces the pressure on the sand, preventing them from sinking. Sharp hooves would increase pressure and cause sinking. The camel is not very light, and it does experience friction. Larger area = less pressure for the same force.

Q3. If the force applied on an object is doubled and the area remains the same, the pressure becomes:
Pressure = Force / Area. If the force is doubled and the area stays the same, the pressure also doubles because pressure is directly proportional to force. Halving, four times, or remaining the same would occur with different changes in area or force.

Q4. Which of the following is an example of force changing both the speed and direction of an object simultaneously?
When a cricket ball is hit for a boundary, the bat applies a force that changes both the speed (it may speed up) and the direction (it goes towards the boundary). A falling ball changes speed but not direction, a car at constant speed changes neither, and a book at rest experiences no change.

Q5. Why is it easier to cut vegetables with a sharp knife than with a blunt one?
A sharp knife has a very small cutting edge area. When the same force is applied, the pressure (Force/Area) is much higher, making it easier to cut. A blunt knife has a larger area, resulting in less pressure. The force applied may be the same; the difference is in area, not friction.

Q6. Two objects of the same mass are placed on a table. Object A has a flat base, and Object B has pointed legs. Which object exerts more pressure on the table?
Pressure = Force / Area. Both objects have the same mass (so the same force = weight). Object B has pointed legs, which have a much smaller area of contact. Smaller area means more pressure. Object A has a flat base with a larger area, so less pressure. Material does not affect the pressure calculation here.

Q7. A person exerts a force of 500 N on the ground while standing. If the total area of his feet is 0.025 m², what pressure does he exert?
Pressure = Force / Area = 500 N / 0.025 m² = 20,000 Pa. 12.5 Pa would be area × force incorrectly, 500 Pa would be force only, and 0.00005 Pa would be area / force. So 20,000 Pa is correct.

Q8. Why does a sharp nail easily penetrate a wooden wall, but a blunt nail does not, even when the same force is applied?
The sharp nail has a pointed tip with a very small area. For the same force, the pressure (Force/Area) is much higher, allowing it to penetrate. A blunt nail has a larger area, so the pressure is lower. Friction is not the main reason; it’s the pressure difference. The material may be the same.

Q9. A diver finds it difficult to dive deep into the sea without proper equipment. Why?
Water pressure increases with depth. At great depths, the pressure is extremely high and can crush the human body. Divers need special equipment (like pressure suits or submersibles) to withstand this pressure. Cold temperatures are an issue but not the primary reason for the difficulty in diving deep.

Q10. Which of the following correctly explains why a straw works to drink a beverage?
When you suck on a straw, you reduce the pressure inside it. The atmospheric pressure on the surface of the liquid is higher, so it pushes the liquid up into the straw. The straw does not “suck” in a physical sense; it is the atmospheric pressure that does the work. Muscular force is not pulling the liquid directly.

Q11. A truck and a car are moving on a road. Which one requires a larger force to stop if both are moving at the same speed?
A truck has much more mass than a car. According to Newton’s Second Law (F = ma), for the same deceleration (change in speed), a larger mass requires a larger force. The road conditions affect friction, but the basic requirement for force to stop depends on mass. The truck, being heavier, needs more force.

Q12. Two magnets are placed with their north poles facing each other. What will happen?
Like poles of magnets repel each other. North-North or South-South will repel. North-South will attract. Since the north poles are facing each other, they will push each other away. They will not attract, not interact (they will interact), or just rotate.

Q13. A plastic ruler is rubbed with wool and brought near small pieces of paper. The paper pieces jump and stick to the ruler. What is the force responsible?
Rubbing a plastic ruler with wool creates static electricity (electrostatic charge). The charged ruler exerts an electrostatic force on the neutral paper pieces, attracting them. Magnetic, gravitational, and frictional forces are not responsible here. The attraction is due to opposite charges being induced.

Q14. Which of the following is an application of atmospheric pressure?
When a syringe plunger is pulled back, it reduces pressure inside the barrel. The atmospheric pressure outside pushes the medicine into the syringe. A car moving uses engine force, a magnet uses magnetic force, and a potter uses muscular force. The syringe is a classic example of atmospheric pressure.

Q15. If the area of contact is doubled and the force is halved, what is the net effect on pressure?
Pressure = Force / Area. If Force is halved (F/2) and Area is doubled (2A), the new pressure = (F/2) / (2A) = F / (4A). This is one-fourth of the original pressure. Doubling, remaining same, or half are not correct.

Q16. Why do mountaineers carry oxygen cylinders while climbing high mountains?
At high altitudes, the atmospheric pressure is lower, so the partial pressure of oxygen is also lower. This makes it difficult to get enough oxygen into the lungs. Mountaineers carry oxygen cylinders to supplement the low oxygen levels. Pressure does not increase; it decreases. Keeping warm or reducing weight are not the primary reasons.

Q17. When a force is applied to a spring, it stretches. If the force is removed, it returns to its original shape. This property is called:
Elasticity is the property of a material to regain its original shape after the deforming force is removed. Plasticity is the property of permanent deformation, friction opposes motion, and inertia is resistance to change in motion. The spring returning to shape is elasticity.

Q18. A person lifts a bucket of water from a well. The force exerted by the person is against which force?
The person is lifting the bucket upward, against the downward gravitational force exerted by the Earth on the bucket. The force exerted by the person is muscular force, but it opposes gravity. Magnetic, electrostatic, and frictional forces are not the forces being opposed here.

Q19. Which of the following statements about friction is correct?
Friction depends on the nature (roughness/smoothness) of the surfaces in contact and the normal force (how hard they are pressed). Friction is not always undesirable (walking, writing), cannot be completely eliminated, and does depend on how hard surfaces are pressed. The correct statement is that it depends on the nature of the surfaces.

Q20. A water tank has two holes at different depths. From which hole will water gush out with greater pressure?
Liquid pressure increases with depth. The hole at the bottom is at a greater depth, so the water pressure there is higher. This means water will gush out with greater force from the bottom hole. Size of the hole affects the amount of water but not the pressure itself.

Q21. Why is it difficult to walk on a slippery floor?
A slippery floor has very low friction. When we walk, we rely on friction to push off and change direction. Reduced friction means less grip, making it difficult to walk without slipping. Gravity does not increase, the floor does not get heavier, and air pressure does not decrease.

Q22. A ship made of iron floats on water, but an iron nail sinks. Why?
A ship floats because it is hollow, containing a lot of air. This makes its overall (average) density less than the density of water. An iron nail is solid, so its density is greater than water, causing it to sink. Surface area affects buoyancy, but the primary reason is density. The ship is heavier than the nail overall but less dense.

Q23. The force of gravity on the Moon is about 1/6th that on Earth. If a person weighs 600 N on Earth, what would be their weight on the Moon?
Weight on the Moon = (Weight on Earth) / 6. 600 N / 6 = 100 N. Mass remains the same (about 60 kg), but weight changes due to different gravity. 600 N is Earth weight, 3600 N would be if Moon had more gravity, and 0 N is incorrect.

Q24. Which of the following is an example of force causing a change in the state of motion from rest to motion?
The hockey player applies a force to a stationary ball, setting it into motion. This is a change from rest to motion. A ball stopping is a change from motion to rest, a spring being compressed is a shape change, and braking a car stops it (motion to rest).

Q25. Why do kites fly high in the sky?
Kites fly because of the aerodynamic force created by the wind. The wind creates a pressure difference above and below the kite, generating lift. Gravity pulls the kite down, but the lift force overcomes it. Magnetic and electrostatic forces are not involved.

Q26. A brick is placed on a table in three different positions: flat, on its side, and on its end. In which position does it exert maximum pressure?
Pressure = Force / Area. The force (weight of the brick) is the same in all positions. The area of contact is smallest when the brick is on its end, so the pressure is maximum. Flat has the largest area (least pressure), and on its side is intermediate. So “on its end” gives maximum pressure.

Q27. A ball is thrown upwards. What forces are acting on it after it leaves the hand?
Once the ball leaves the hand, the muscular force is no longer acting. The only forces acting on it are the gravitational force (pulling it down) and air resistance (opposing its motion). Friction is not a direct force on the ball in this context (air resistance is a form of friction).

Q28. The treads (grooves) on car tyres are designed to:
Treads on tyres increase friction between the tyre and the road, providing better grip and preventing skidding. This is especially important in wet or slippery conditions. They do not increase pressure on the road, decrease friction, or are just for looks. The grooves channel water away and increase grip.

Q29. Which of the following correctly describes the direction of pressure exerted by a gas enclosed in a container?
Gases exert pressure equally in all directions on the walls of their container. The particles collide with all surfaces randomly, resulting in uniform pressure. Liquids also exert pressure in all directions. Solids exert pressure in the direction of the applied force.

Q30. A stone tied to a string is whirled in a circle. The force that keeps it moving in a circular path is called:
The force that keeps an object moving in a circular path is called centripetal force (meaning “centre-seeking”). In this case, the tension in the string provides the centripetal force. Gravity, friction, and muscular force (the initial push) are not the forces keeping it in the circle.

Q31. Why does a porter place a round piece of cloth on his head while carrying a heavy load?
The cloth increases the area of contact on the porter’s head. This spreads the weight (force) over a larger area, reducing the pressure (P = F/A). This prevents injury and makes carrying the load more comfortable. The weight of the load is not reduced.

Q32. Which of the following is not a non-contact force?
Pedaling a bicycle involves muscular force, which is a contact force (the cyclist is in contact with the pedals). A compass needle deflecting (magnetic), a balloon sticking (electrostatic), and a leaf falling (gravitational) are all non-contact forces. So the cyclist pedaling is the contact force.

Q33. Two objects are kept on a table. Object P has a mass of 5 kg and an area of 2 m². Object Q has a mass of 10 kg and an area of 5 m². Which object exerts more pressure? (Take g = 10 m/s²)
Force = mass × g.
For P: Force = 5 × 10 = 50 N. Pressure = 50 / 2 = 25 Pa.
For Q: Force = 10 × 10 = 100 N. Pressure = 100 / 5 = 20 Pa.
Object P exerts more pressure (25 Pa vs 20 Pa). So Object P is correct.

Q34. Why do we slip on a banana peel?
A banana peel reduces friction between our feet and the ground because it acts as a lubricant. This reduced friction makes it difficult to maintain grip, causing us to slip. It does not increase friction, gravity, or create magnetic force.

Q35. A hole is made in a plastic bottle filled with water near its bottom. Water comes out with high pressure. If three holes are made at the same height on different sides, what will be observed?
At the same depth, the pressure in a liquid is the same in all directions. Therefore, water will gush out with equal force and speed from all three holes, regardless of their direction. This demonstrates that liquid pressure acts equally in all directions at a given depth.

Q36. A person pushes a wall but the wall does not move. Which of the following statements is correct?
According to Newton’s Third Law, for every action, there is an equal and opposite reaction. When the person pushes the wall, the wall pushes back with an equal and opposite force. The wall does not move because the forces are balanced, but the wall does apply a force back on the person.

Q37. Which of the following correctly explains why ink is filled in a fountain pen?
When the lever of a fountain pen is pressed, air is expelled, reducing the pressure inside the pen. When the lever is released, the atmospheric pressure outside is greater and pushes the ink into the pen. This is the same principle as a syringe. Gravity and magnetic force are not involved.

Q38. A ball is dropped from a height. Its speed increases continuously until it hits the ground. This is because:
The force acting on the ball is gravity, which is constant and acts in the direction of motion (downward). This constant force causes a constant acceleration (g), so the speed of the ball increases continuously. The force is not decreasing, and friction (air resistance) is increasing but is not the primary reason for the speed increase.

Q39. A wooden block is placed on a table. A spring balance is attached to it and pulled. The block starts moving only when the spring balance shows a reading of 5 N. What does this reading indicate?
The block starts moving when the applied force exceeds the maximum static friction. The reading of 5 N indicates the maximum static friction force that must be overcome to set the block in motion. The weight of the block is different, and kinetic friction is lower than static friction.

Q40. Why are the soles of shoes and the treads of tyres made with grooves?
Grooves on soles and tyre treads increase friction by providing better grip, especially on wet or slippery surfaces. They channel water away and increase the surface roughness. This is for safety and control, not for increasing pressure, reducing weight, or just aesthetics.

Q41. A hydraulic lift works on which principle related to pressure?
Hydraulic lifts work on Pascal’s principle, which states that when pressure is applied to an enclosed liquid, it is transmitted equally and undiminished in all directions. This allows a small force on a small piston to produce a large force on a larger piston. The other options are not the correct principle for a hydraulic lift.

Q42. When a fast-moving cricket ball hits a stationary wicket, the wicket falls. This shows that:
The ball applies a force on the wicket, which is stationary. This force sets the wicket into motion (falling). This is a clear example of force changing an object’s state from rest to motion. It also changes the shape slightly, but the primary effect is the change in motion.

Q43. Which of the following is an example of the force of friction being useful?
Writing with a pen on paper relies on friction between the pen tip and the paper. Without friction, the pen would not leave a mark. Wearing out of parts, heat generation, and difficulty in sliding are examples of friction being undesirable or problematic.

Q44. The value of atmospheric pressure is 10⁵ Pa. If a person’s head has an area of 0.05 m², what is the force exerted by the atmosphere on the head?
Force = Pressure × Area = 10⁵ Pa × 0.05 m² = 5000 N. This is the force exerted by the atmosphere on the head. 2,000,000 N is too high, 2,000 N is incorrect, and 200 N is also incorrect. So 5000 N is correct.

Q45. A ball is thrown vertically upwards. At its highest point, which of the following is true?
At the highest point, the ball’s speed is momentarily zero. However, the gravitational force is still acting on it, pulling it back down. The force is not zero; it is constant. Speed is minimum (zero) at this point, not maximum.

Q46. Why are heavy trucks fitted with many wheels?
Heavy trucks have many wheels to increase the area of contact with the road. This spreads the weight over a larger area, reducing the pressure on the road and preventing damage to the road surface. It is not for increasing pressure, looks, or speed.

Q47. Two magnets are placed on a table with their south poles facing each other. What will be the nature of the force between them?
Like poles of magnets repel each other. South-South will repel. North-South would attract. Gravitational force is always attractive but is negligible here. The magnetic force between the south poles is repulsive.

Q48. A simple barometer uses a column of mercury to measure atmospheric pressure. If we use water instead of mercury (which is 13.6 times less dense), what would happen to the height of the water column?
Atmospheric pressure supports a column of liquid. Since pressure = ρgh, for the same atmospheric pressure, the height (h) is inversely proportional to density (ρ). Water is 13.6 times less dense than mercury, so the height of the water column would be 13.6 times greater than the mercury column (about 10.3 m). So the height would be larger, not smaller or the same.

Q49. When a moving car stops suddenly, the passengers tend to lurch forward. This is due to:
According to Newton’s First Law, an object in motion tends to stay in motion. When the car stops suddenly, the passengers’ bodies continue to move forward due to their inertia. This is why they lurch forward. Friction, gravity, and pressure are not the primary causes of this effect.

Q50. Which of the following correctly compares the pressure exerted by a solid, a liquid, and a gas?
Solids exert pressure in the direction of the applied force (e.g., a book pressing down on a table). Liquids and gases exert pressure equally in all directions (Pascal’s principle). This is the correct comparison. Gases and liquids do not exert pressure only downwards or upwards; they act in all directions.