Olympiad Test: Force And Pressure - 2 - Free MCQ with solutions Class 8

• Interacting Objects: When two objects interact with each other, they exert force on each other. This force can cause a change in the motion of the objects.


• Force as a Result of Interaction: Forces only come into play when objects interact with each other. If there is no interaction between the objects, there will be no force acting on them.


• Types of Interactions: Interactions between objects can be gravitational, electromagnetic, or nuclear. These interactions determine the type and magnitude of the force exerted.


• Effect of Interaction: The interaction between objects can lead to acceleration, deceleration, or a change in direction of motion. This is a result of the forces acting on the objects.

• Contact Force: Friction is a contact force that occurs between two surfaces in contact with each other.


• Direction of Motion: The force of friction can act in the same direction as the motion of an object or in the opposite direction, depending on the situation.


• Surface Smoothness: The magnitude of friction is small if the surfaces in contact are smooth, as there is less resistance to motion.


• Features: The force of friction exhibits all the mentioned features - it is a contact force, acts in the same or opposite direction to motion, and varies based on the smoothness of surfaces.

Therefore, the correct answer is option D, as the force of friction possesses all these characteristics. It is important to understand these aspects of friction when analyzing the interactions between objects and surfaces in physics.

Dynamics, branch of physical science and subdivision of mechanics that is concerned with the motion of material objects in relation to the physical factors that affect them: force, mass, momentum, energy.

• Magnitude: Force is a vector quantity, which means it has both magnitude and direction. The magnitude of a force is represented by the length of the arrow in a force diagram.


• Direction: Another characteristic of force is that it has a specific direction. This is important because forces only affect objects in the direction they are applied.


• Scalar: Force is not a scalar quantity. It is a vector quantity because it has both magnitude and direction. Scalars only have magnitude.


• Changes the state of motion: One of the key properties of force is that it can change the state of motion of an object. This can include starting, stopping, speeding up, or slowing down an object.

• Change in Speed: When force is applied to an object, it can change the speed at which the object is moving. The object can either speed up, slow down, or maintain a constant speed depending on the direction and magnitude of the force applied.


• Change in Direction: Force can also change the direction of motion of an object. For example, when a force is applied to a moving object in a certain direction, it can change the object's path of motion.


• Change in State of Rest or Motion: Force can change the state of rest or motion of an object. If a force is applied to an object at rest, it can set the object in motion. Conversely, if a force is applied to a moving object, it can bring the object to rest.


• Change in Dimension or Shape: In some cases, force can also change the dimension or shape of an object. For example, when a force is applied to a flexible object, it can cause the object to deform or change its shape.

• All of these Effects: In conclusion, force can have various effects on an object, including changing its speed, direction, state of rest or motion, as well as its dimension or shape. Therefore, the correct answer is option D: All of these.

A barometer is a scientific instrument used to measure atmospheric pressure, also called barometric pressure.

• Forces acting on the football: Two forces are acting on the football simultaneously.


• Remains static: Despite the two forces acting on it, the football remains static, i.e., it does not move.


• Definition of balanced force: When two forces of equal magnitude act in opposite directions on an object, the object remains at rest or continues to move at a constant velocity. This is known as a balanced force.


• Equilibrium: The state of balance between the two forces acting on the football is called equilibrium.


• Static force: The football is under the influence of static force, which keeps it in a state of rest despite the two forces acting on it.

• Atmospheric Pressure: Atmospheric pressure is the force per unit area exerted on a surface by the weight of the air above that surface in the Earth's atmosphere. It is commonly measured in units of pascals (Pa) or newtons per square meter (N/m²).


• Value at Sea Level: The value of atmospheric pressure at sea level on the surface of the Earth is approximately 1.013 × 10⁵ N/m².


• Correct Answer: Option A:

  1.013 × 10⁵ N/m²

  is the correct value for atmospheric pressure at sea level.

• Unbalanced forces: When a set of forces applied on an object results in the movement or acceleration of the body, these forces are called unbalanced forces.


• Movement or acceleration: Unbalanced forces cause objects to move or accelerate in the direction of the resultant force.


• Net force: The net force acting on an object is the sum of all the individual forces acting on it. If the net force is not zero, then the forces are unbalanced.


• Newton's first law: According to Newton's first law of motion, an object will remain at rest or in uniform motion unless acted upon by an external force. Unbalanced forces are necessary to change the state of motion of an object.


• Examples: Some examples of unbalanced forces include pushing a car to make it move, kicking a ball to accelerate it, or pulling an object with a rope to change its direction.

• Contact Forces: Contact forces are forces that result from the interaction between two objects that are physically touching each other. Muscular force and friction force are examples of contact forces because they require direct contact between objects to occur.


• Gravitational Forces: Gravitational forces are forces that act between two objects due to their mass. Muscular force and friction force are not examples of gravitational forces because they do not involve the mass of the objects.


• Magnetic Forces: Magnetic forces are forces that act between magnetic objects. Muscular force and friction force are not examples of magnetic forces because they do not involve magnetism.


• Distant Forces: Distant forces are forces that act between objects that are not in direct contact with each other. Muscular force and friction force are not examples of distant forces because they require direct contact to occur.

Therefore, the correct answer is A: contact forces.

• Given force applied = 1N


• We need to find the mass that can be held in our hand

• Using the formula F = ma, where F is the force, m is the mass, and a is the acceleration


• Given force F = 1N and acceleration a = 9.8 m/s^2 (acceleration due to gravity)


• Substitute the values in the formula to find the mass: 1 = m * 9.8


• Solving for m, we get m = 1/9.8


• So, the mass that can be held in our hand is approximately 0.102 kg or 102g

• Therefore, by applying a force of 1N, we can hold a mass of approximately 100g in our hand

• Attractive: Electrostatic forces can be attractive when opposite charges interact. For example, a positively charged object will attract a negatively charged object.


• Repulsive: Electrostatic forces can be repulsive when like charges interact. For instance, two positively charged objects will repel each other.


• Either (a) or (b): In some cases, electrostatic forces can be either attractive or repulsive, depending on the charges involved.


• Neither (a) nor (b): This option is not correct as electrostatic forces will always be either attractive or repulsive based on the charges present.

Therefore, the correct answer is option C: either (a) or (b), as electrostatic forces can be both attractive and repulsive depending on the charges involved.

Pressure exerted by a block in standing position is more than the pressure exerted by the block in lying position.

A barometer is the instrument specifically designed to measure atmospheric pressure. It helps in various applications, including weather forecasting and altitude measurement.

• Barometer: A device that measures the pressure exerted by the atmosphere.
• Types: There are two main types of barometers:
  • Mercury Barometer: Uses mercury in a glass tube; the height of the mercury column indicates pressure.
  • Altimeter: A type of barometer used in aviation to measure altitude based on atmospheric pressure.
• Importance: Understanding atmospheric pressure is crucial for predicting weather changes and ensuring safe flight operations.

• Pressure of water: The pressure of water alone cannot explain the rise of water in the dropper. The pressure of water would push the water out of the dropper, not make it rise.


• Atmospheric pressure: Atmospheric pressure is the force exerted by the weight of the air above. When we press the bulb of the dropper and release it, the air inside the dropper escapes, creating a low-pressure area. This low-pressure area allows the higher atmospheric pressure outside the dropper to push the water up into the dropper.


• Gravity: Gravity plays a role in pulling the water down, but it is not the primary force causing the water to rise in the dropper.


• Shape of rubber bulb: The shape of the rubber bulb helps in creating pressure inside the dropper when it is squeezed, but it is not the main reason for the water rising in the dropper.