Class 10 Science SEE Guide | Unit - 8 Pressure guide 2080

Class 10 Science SEE Guide

Unit - 8 Pressure Guide

Exercise

1. Choose the correct option for the following questions:

(a) On which law/principle is a lactometer based?

(i) Pascal's law

(ii) Law of Gravitation

(iii) Archimedes' principle

(iv) Newton's law

Answer 👉 (iii) Archimedes' principle

(b) What is the condition for flying a hydrogen balloon upwards in the air?

(i) weight of the balloon = weight of air displaced

(ii) weight of balloon > weight of air displaced

(iii) weight of the balloon = volume of air displaced

(iv) weight of balloon < weight of air displaced

Answer 👉 (iv) weight of balloon < weight of air displaced

( c) In a hydraulic machine, if the cross-sectional area of the larger piston is twice the area of the smaller piston, what is the correct group of the weights on the smaller piston (W1) and the larger piston (W2 ) to keep the machine balanced?

(i ) W1 = 4 N, W = 2 N 2

(iil w1 = 5 N, w2 = 10 N

(iii) W 1 = 2 N, W 2 = 1 N

(iv) W 1 = 3 N, W2 = 1.5 N

Answer 👉 (i ) W1 = 4 N, W = 2 N 2

( d) When an object is suspended using spring balance in air, water and glycerin, the weight is founded to be W1, W2, and W3 respectively. What will be the weight of the object in those mediums in increasing order?

(i ) w 1 < w 2 < w 3

(ii) w 2 < w 1 < w 3

(iii) W 3 < w2 < w1

Answer 👉 (ii) w 2 < w 1 < w 3

( e) When a ship enters a river from a sea, it was found to sink more than before. What is the reason for this?

(i) The temperature of seawater is more than that of river water

(ii) the density of seawater is more than that of river water

(iii) the temperature of seawater is less than that of river water

(iv) the density of seawater is less than that of river water

Answer 👉 (ii) the density of seawater is more than that of river water

(f) Which one of the following statements is correct for a hand pushing a ball into the water as shown in the given figure?

(i) Equal pressure acts on all parts of the ball under the water

(ii) the more the ball is pushed into the water, the lesser the upthrust it experiences

(iii) the pressure on the ball acts only in the upward direction

(iv) the upthrust on the ball increases until it completely sinks into the water

Answer 👉 (ii) the more the ball is pushed into the water, the lesser the upthrust it experiences

(g) If the same magnitude of upthrust acts on the three cubical balls made up of different materials on keeping them in water, which one of the following quantities is equal for them?

(i) density

(iii) volume

(ii) weight

(iv) mass

Answer 👉 (iii) volume

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2. Differentiate between:

(a) pressure and upthrust

Answer 👉

Pressure refers to the force applied per unit area. It is the result of the perpendicular force exerted on an object by a fluid or a solid surface it is in contact with.
Upthrust, also known as buoyant force, is the upward force exerted on an object immersed in a fluid. It is equal to the weight of the fluid displaced by the object.

The main difference between pressure and upthrust is that pressure acts in all directions, both upward and downward, while upthrust acts only in the upward direction. Pressure is dependent on the depth and density of the fluid, while upthrust is dependent on the volume of the object and the density of the fluid.

(b) the reason for a steel pin sinking in water and a steel plate floating on water

Answer 👉 Steel pin sinking in water and steel plate floating on water:

A steel pin sinks in water because its density is greater than the density of water. The weight of the steel pin is greater than the buoyant force exerted on it, causing it to sink.
A steel plate floats on water because its density is less than the density of water. The weight of the steel plate is less than the buoyant force exerted on it, allowing it to float.
The difference in the sinking and floating behavior of the steel pin and steel plate is due to their densities. The steel pin has a higher density, while the steel plate has a lower density compared to water.

(c) the process of a hot air balloon sinking and rising in the air

Answer 👉

When a hot air balloon is sinking, it means that the air inside the balloon is cooler than the surrounding air. Cooler air is denser than the surrounding air, causing the balloon to descend.
When a hot air balloon is rising, it means that the air inside the balloon is hotter than the surrounding air. Hotter air is less dense than the surrounding air, creating buoyant force and causing the balloon to ascend.

The sinking and rising of a hot air balloon are determined by the difference in density between the air inside the balloon and the surrounding air. When the temperature inside the balloon changes, it affects the density of the air, resulting in the balloon either sinking or rising.

3. Give a reason for

(a) A special type of oil is used in hydraulic brakes.

Answer 👉 A special type of oil is used in hydraulic brakes because it is non-compressible. Hydraulic brakes work on the principle of transmitting force through a fluid. When the brake pedal is pressed, the force is transferred to the brake fluid, which then applies pressure to the brake system. The non-compressible nature of the oil ensures that the force is transmitted effectively and instantly, allowing for quick and efficient braking.

(b) A wooden cork dipped below the surface of the water by applying force with a finger comes to the surface when the finger is removed.

Answer 👉 When a wooden cork is dipped below the surface of the water by applying force with a finger and then released, it comes to the surface because of the buoyant force. The buoyant force is the upward force exerted on an object submerged in a fluid, and it is equal to the weight of the displaced fluid. When the finger is removed, the cork experiences an upward buoyant force that exceeds its weight, causing it to rise to the surface of the water.

(c) We feel lighter while floating on water.

Answer 👉 We feel lighter while floating on water because of the buoyant force. When a person floats on water, their body displaces an amount of water equal to their weight. The buoyant force exerted by the water on the person is equal to the weight of the displaced water, and it acts in the upward direction. This upward force counteracts a portion of the person's weight, making them feel lighter.

(d) Onlifting a stone submerged in water, it feels heavier when it comes out of the water.

Answer 👉 When lifting a stone submerged in water, it feels heavier when it comes out of the water because the buoyant force decreases. When the stone is submerged in water, it experiences an upward buoyant force equal to the weight of the water it displaces. However, when it is lifted out of the water, the buoyant force decreases significantly as it is no longer immersed in the water. Therefore, the stone feels heavier when it is lifted out of the water due to the absence of the buoyant force.

(e) Itis easier to float in the Dead Sea than in a swimming pool, (the density of water in the Dead Sea is 1240kg/m?).

Answer 👉 It is easier to float in the Dead Sea than in a swimming pool because of the higher density of the water in the Dead Sea. The density of the water affects the buoyant force experienced by an object. In the Dead Sea, the water has a higher density compared to a swimming pool. Higher density means a greater buoyant force, which makes it easier for objects, including human bodies, to float on the water's surface.

(f) If more passengers climb a boat than its maximum capacity, the boat is likely to sink.

Answer 👉 If more passengers climb a boat than its maximum capacity, the boat is likely to sink because it exceeds its buoyant force limit. Every boat has a maximum carrying capacity, determined by factors such as its design and buoyancy. If the number of passengers exceeds this capacity, the total weight of the passengers and the boat may become greater than the buoyant force exerted by the water. This imbalance can cause the boat to sink as the buoyant force is no longer sufficient to support the weight of the overloaded boat.

4. Answers the following questions:

(a) State Pascal's law.

Answer 👉 Pascal's law states that when pressure is applied to a fluid in a confined space, the pressure is transmitted equally in all directions and to all parts of the fluid and container.

(b) Write any two applications of Pascal's law in daily life.

Answer 👉 Two applications of Pascal's law in daily life are:

Hydraulic brakes: Pascal's law is utilized in hydraulic braking systems found in vehicles. When the brake pedal is pressed, it applies pressure to a small piston in the master cylinder, which is transmitted through the hydraulic fluid to larger pistons in the wheel cylinders. This amplifies the force, allowing efficient braking.
Hydraulic lifts: Many car repair shops use hydraulic lifts that operate based on Pascal's law. By applying a small force on a small piston, the pressure is transmitted through the hydraulic fluid to a larger piston, resulting in a multiplied force that can lift heavy objects.

(c) What is a hydraulic machine?

Answer 👉 A hydraulic machine is a device that uses the principles of Pascal's law to generate, control, or transmit forces using a confined fluid. It typically consists of pistons, cylinders, valves, and a fluid medium (often oil or water). Hydraulic machines are widely used in various applications such as car lifts, hydraulic presses, cranes, and construction equipment.

( d) State Archimedes' principle.

Answer 👉 Archimedes' principle states that when an object is immersed in a fluid, it experiences an upward buoyant force equal to the weight of the fluid it displaces. This principle explains why objects float or sink in fluids and is based on the concept of buoyancy.

( e) What is upthrust?

Answer 👉 Upthrust, also known as buoyant force or buoyancy, is the upward force exerted on an object submerged or partially submerged in a fluid. It is equal to the weight of the fluid displaced by the object. Upthrust acts in the opposite direction to gravity and is responsible for the apparent loss of weight of an object when immersed in a fluid.

(f) Mention the forces acting on a floating object and their directions.

Answer 👉 The forces acting on a floating object are:

Weight: The force exerted by the object due to gravity, acting vertically downward.
Buoyant force: The upward force exerted by the fluid on the object, opposing the weight. It is equal to the weight of the fluid displaced by the object.

(g) State the law of floatation.

Answer 👉 The law of floatation states that a floating object displaces its own weight of the fluid in which it floats. In other words, the weight of the object is equal to the weight of the fluid it displaces. If the weight of the object is less than the weight of the fluid it displaces, the object will float.

(h) Write any two applications of Archimedes' Principle.

Answer 👉 Two applications of Archimedes' principle are:

Ships and boats: The design and buoyancy of ships and boats are based on Archimedes' principle. By ensuring that the weight of the ship is less than the weight of the water it displaces, the ship floats and remains stable.
Hot air balloons: Hot air balloons utilize Archimedes' principle to float in the air. By heating the air inside the balloon, it becomes less dense than the surrounding air, resulting in a buoyant force greater than the weight of the balloon and its contents, causing it to rise.

(i) Explain, with a figure, the cause of the production of upthrust.

Answer 👉 The production of upthrust is caused by the pressure difference between the top and bottom surfaces of an immersed object. When an object is submerged in a fluid, the pressure exerted by the fluid increases with depth. The pressure at the bottom of the object is greater than the pressure at the top. This pressure difference results in an upward force, known as upthrust or buoyant force, acting on the object. The figure below illustrates this concept:

↑ Upthrust (Buoyant Force)

| ↑

| |

| Object submerged in fluid

| |

| ↓

↓

Fluid

Class 10 Science SEE Guide | Unit - 8 Pressure guide 2080

(j) When a stone is dropped into the water, it sinks. Does this happen because of the absence of upthrust?

Answer 👉 No, the sinking of a stone when dropped into the water is not due to the absence of upthrust. In fact, the stone sinks because its density is greater than the density of the water. According to Archimedes' principle, an object sinks if its weight is greater than the buoyant force acting on it. Upthrust is always present in a fluid, but if the weight of the object is greater than the upthrust, the object will sink.

(k) A person is trying to lift a stone of SOON keeping it on the smaller piston of a hydraulic machine by applying a force on the larger piston. What suggestion would you give him/ her so that he/she can lift the load easily? Explain, with an appropriate figure, the process of increasing the force in the hydraulic machine.

Answer 👉 If a person is trying to lift a stone of 500 N using a hydraulic machine, they can achieve an easier lift by increasing the force applied on the larger piston. This can be done by increasing the area of the larger piston compared to the smaller piston. The hydraulic machine works based on Pascal's law, which states that pressure is transmitted equally in a confined fluid. By increasing the area of the larger piston, the force exerted on it is multiplied, resulting in a larger force acting on the smaller piston. The figure below illustrates this process:

Large Piston (Area: A2)

_____________________

| |

| Fluid |

|_____________________|

Small Piston (Area: A1)

By increasing the area (A2) of the larger piston, the force exerted on it (F2) is increased. This increased force is transmitted through the fluid and exerts a larger force (F1) on the smaller piston. Therefore, the person can easily lift the stone by applying a smaller force on the larger piston.

(l) Substances with a density greater than the density of the liquid sink in it. Is this statement always true? Justify with an example.

Answer 👉 The statement "substances with a density greater than the density of the liquid sink in it" is not always true. Whether an object sinks or floats in a liquid depends on the relationship between the densities of the object and the liquid. If the density of the object is greater than the density of the liquid, the object will sink. However, if the density of the object is less than the density of the liquid, the object will float. For example, a ship made of steel has a greater density than water, yet it floats. This is because the ship is designed in a way that its shape and volume displace a large amount of water, creating enough upthrust to balance its weight. So, it's not solely the density of the object that determines whether it sinks or floats, but rather the comparison of densities between the object and the liquid.

(m) Two balloons, one filled with air and the other with hydrogen, look identical. What difference can be noticed when they are released into the air? Explain with reasons.

Answer 👉 When released into the air, two balloons, one filled with air and the other with hydrogen, will behave differently due to the difference in densities of the gases. The hydrogen-filled balloon will rise in the air, while the air-filled balloon will tend to stay at the same level or may descend slowly. This difference occurs because hydrogen gas is less dense than air, resulting in a greater buoyant force acting on the hydrogen-filled balloon. On the other hand, air has a density similar to the surrounding air, so there is little or no buoyant force acting on the air-filled balloon.

(n) An object is suspending /floating just below the surface of the water. If the amount of salt dissolving in the water goes on increasing, what change will occur in the position of the balloon? Explain with reasons.

Answer 👉 If an object is floating or suspending just below the surface of the water, increasing the amount of salt dissolving in the water will make the water denser. As a result, the buoyant force acting on the object will increase, causing it to rise or float higher in the water. The increase in salt concentration leads to an increase in the density of the water, which enhances the buoyancy effect and raises the position of the floating object.