Forces MCQ Quiz - Objective Question with Answer for Forces - Download Free PDF

The correct answer is cohesive force.

• The force of attraction between the same kind of molecules is called the force of cohesion.
• The force of attraction between different kinds of molecules is called the force of adhesion.

Key Points

• The cohesion force of fine particles is important for the growth and strength of green granules.
  • The former affects the size distribution of final granules formed, while the latter has a direct impact on the permeability of a packed granule bed. 
• The cohesive forces between molecules down into a liquid are shared with all neighbouring atoms.

Additional Information

• Viscosity:
  • Viscosity is the resistance of a fluid (liquid or gas) to a change in shape or movement of neighbouring portions relative to one another.
  • ​Viscosity is a measure of a fluid's resistance to flow. The SI unit of viscosity is poiseuille (PI).
  • Its other units are newton-second per square meter (N s m-2) or pascal-second (Pa s.). The dimensional formula of viscosity is (ML-1T-1). 
• Surface tension:
  • Surface tension is the tendency of fluid surfaces to shrink into the minimum surface area possible.​
  • Surface tension is typically measured in dynes/cm, the force in dynes is required to break a film of length 1 cm.
• Adhesive force:
  • The adhesion forces can be one of the results of electrostatic forces which are exerted on different substances.​
  • Adhesion is generally the force of attraction present between the water molecules and the walls of xylem vessels.

The correct answer is Weight of the object.

Key Points

• The force with which the Earth attracts an object is called the weight of the object.
• Weight is determined by the gravitational force acting on the object's mass.
• The formula for weight is W = m × g, where 'm' is the mass of the object, and 'g' is the acceleration due to gravity (approximately 9.8 m/s² on Earth).
• Weight is a vector quantity, meaning it has both magnitude and direction; its direction is always toward the center of the Earth.
• Unlike mass, weight can change depending on the gravitational field strength (e.g., it is less on the Moon due to lower gravity).

Additional Information

• Mass: The quantity of matter in an object, measured in kilograms (kg). Mass is a scalar quantity and remains constant regardless of location.
• Density: Defined as mass per unit volume, represented by the formula ρ = m/V. It is a measure of how much mass is packed into a given volume.
• Gravitational force: A fundamental force of nature that attracts two bodies with mass toward each other. The gravitational force is responsible for the weight of objects on Earth.
• Magnitude: Refers to the size or quantity of a vector, such as force. It does not specify the nature or source of the force.
• On celestial bodies other than Earth, the gravitational acceleration 'g' differs, causing weight variations. For instance, on the Moon, gravity is approximately 1/6th that of Earth.

The correct answer is 400 W.

Key Points

• The power required to lift a mass is calculated using the formula P = (m × g × h) / t, where m is mass, g is gravitational acceleration, h is height, and t is time.
• Given: m = 50 kg, g = 10 m/s², h = 8 m, and t = 10 s.
• Substituting values: P = (50 × 10 × 8) / 10 = 400 W.
• The minimum power required for lifting the mass is thus 400 Watts.
• Option 1 (400 W) is correct as per the calculation.

Additional Information

• Power: Power is the rate at which work is done or energy is transferred. The SI unit of power is the Watt (W).
• Work: Work is done when a force is applied to an object and it moves in the direction of the force. The formula for work is W = F × d, where F is force and d is displacement.
• Gravitational Force: The force exerted by the Earth on objects due to gravity. The acceleration due to gravity (g) is approximately 9.8 m/s², but for simplicity in calculations, it is often taken as 10 m/s².
• Energy: Energy is the capacity to perform work. Lifting an object vertically against gravity requires energy equal to the product of its weight and the height to which it is lifted.
• Efficiency: In practical applications, the power calculated is the theoretical minimum, assuming 100% efficiency. Real systems may require more power due to energy losses.

The correct answer is 4) 1, 2 and 3.

Key Points

• Gravitational force contributes to mechanical weathering through processes like landslides, rockfall, and soil creep, breaking down rocks.
• Expansion force, such as thermal expansion, causes rocks to crack due to temperature changes, where materials expand and contract repeatedly.
• Water pressure, especially in freeze-thaw cycles, exerts significant force on rock crevices, leading to their fragmentation over time.
• These forces, acting individually or in combination, are key drivers of the physical breakdown of rocks into smaller particles without changing their chemical composition.
• Mechanical weathering is crucial for soil formation and plays a vital role in shaping the Earth's surface.

Additional Information

• Mechanical Weathering: It is the process of breaking down rocks into smaller fragments through physical forces without altering their chemical composition.
• Freeze-Thaw Weathering: Occurs when water enters cracks in rocks, freezes, and expands, leading to rock disintegration.
• Thermal Expansion: Rocks expand when heated and contract when cooled. Repeated cycles of expansion and contraction can cause them to fracture.
• Abrasion: Physical scraping of rocks caused by particles carried by wind, water, or ice, leading to surface erosion.
• Unloading and Exfoliation: Removal of overlying material reduces pressure on rocks, causing outer layers to peel off in sheets, a process known as exfoliation.

The Correct answer is Zero.

Key Points

• Balanced forces are equal in magnitude and opposite in direction.
• When balanced forces act on an object, they cancel each other out.
• This results in no net force acting on the object.
• As a result, the object remains in its current state of motion, either staying at rest or continuing to move with a constant velocity.
• According to Newton's First Law of Motion, an object will remain at rest or in uniform motion unless acted upon by an unbalanced force.
• Therefore, when balanced forces are applied, the net force is zero, and there is no change in the object's motion.

 Additional Information

• Equal to the mass of the object
  • The mass of an object is a measure of the amount of matter it contains and is not related to the net force acting on the object.
  • Mass remains constant regardless of the forces applied to the object.
• Equal to acceleration
  • The net force acting on an object is equal to the mass of the object multiplied by its acceleration (F = ma), according to Newton's Second Law of Motion.
  • This option is incorrect because it does not consider the condition of balanced forces, which result in zero net force and no acceleration.
• Infinite
  • An infinite force is an unrealistic and impractical concept in physics.
  • Balanced forces do not imply an infinite force but rather equal and opposite forces that cancel each other out.

The correct option is Thrust Force.

Key Points

• Thrust is the force that moves an aircraft through the air.
• Thrust is used to overcome the drag of an airplane, and to overcome the weight of a rocket.

Additional Information 

• Drag Force: The air resistance that tends to slow the forward movement of an airplane. 
• Gravity Force: The force that pulls all objects towards the earth. 
• Lift Force: The upward force that is created by the movement of air above and below a wing. Air flows faster above the wing and slower below the wing, creating a difference in pressure that tends to keep an airplane flying.

CONCEPT:

• Work-energy theorem: It states that the sum of work done by all the forces acting on a body is equal to the change in the kinetic energy of the body i.e.,

Work done by all the forces = Kf - Ki

\(W = \frac{1}{2}m{v^2} - \frac{1}{2}m{u^2} = {\bf{Δ }}K\)

Where v = final velocity, u = initial velocity and m = mass of the body

EXPLANATION:

Given that:

• Mass of the Object (m) = 1 kg
• Initial velocity of the object (u) = 4m/s
• Final velocity of the object (v) = 8m/s
• Total net work is done W _(net) = Kinetic energy (During final velocity) – Kinetic Energy (During Initial Velocity).
• Now by substituting the values in the above equation, we get

W_(net) = ½ mv² – ½ mu²

= ½ (1)×(8)² – ½ (1)×(4)²

= 32 - 8 Joule

= 24 Joules.

• Therefore, the total work done by the force is 24 J.

The correct answer is ​Tension force.

Key Points

• A car towing another car with a chain is an example of a Tension force.
• The force of tension is defined as the force which is transmitted by rope, string, or wire when pulled by forces acting from opposite sides.
• The force of stress is directed over the length of the wire and at the ends pulls energy evenly on the bodies.
• Any physical object that is in contact with each other exerts some force.
• Cables and ropes can be used to exert forces since they can easily move a force over a given distance (e.g. the length of the rope). 

Additional Information

• Frictional Force refers to the force produced by two surfaces that come in contact and slide against each other.
• An applied force is a force that a human or some other object applies to an entity. If an individual moves a desk across the room, then an applied force acts on the object.
• The Normal force is the force of support exerted on an object which is in contact with another stable object. It always occurs perpendicular to the surface.

CONCEPT:

• Work: Work is said to be done by a force when the body is displaced actually through some distance in the direction of the applied force.
• Since the body is being displaced in the direction of F, therefore work done by the force in displacing the body through a distance s is given by:

\(W = \vec F \cdot \vec s\)

• Thus work done by a force is equal to the scalar or dot product of the force and the displacement of the body.

EXPLANATION:

Given that:

Mass (m) = 25 kg.

Distance (s) = 15 m.

Work (W) = 480 J.

Using equation:

\(Work = Force × Distance\)

∴ 480 = F × 15

F = \(480\over15\)= \(32\ N\)

Force = 32 N.

The correct answer is F/16.

Given that, 

m1 = m1/4,

m2 = m2/4,

keeping d = constant.

As F α (m1 × m2 ) /r2

Then the new Force is 

Fnew = G (m1/4) × (m2/4)/r2  = F/16

The correct option is F/16.

​Key Points

• Gravitational force: It states that the force of attraction between any two bodies is directly proportional to the product of their masses and is inversely proportional to the square of the distance between them.
  • ​It can also be defined as the universal force of attraction, which is acting between objects, is known as the gravitational force.​
  • F = Gm1m2/r2
  • where F = gravitational force between two bodies, m1 = mass of the first body, m2 = mass of the second body, r = distance between the centres of two bodies.

We have been given

a = –10 m/s²; t = 3 s and v = 0 m/s.

v = u + at 

0 = u + (–10 m/s²) × 3s

u = 30 m/s

s = u t + 1/2 a t²

= 30 × 3 + 1/2 × -10 × 3 × 3

= 90 - 45

= 45 m

• This constant tug on the Moon as it moves around the Earth is called a "centripetal" force. This force is balanced by the "centrifugal" force, that pulls on the Earth and keeps the moon in motion.
• The moon revolves around earth because of Earth’s gravitational force.
• The Gravitational force of Earth tends to attract Moon.
• The centripetal force acts on a body, moving in a circular path, and is directed towards the center around which the body is moving.

→ Given data -

• Mass, m = 40 kg

Height, h = 5m

Time, t = 4s

• Work done, W = mgh

W = 40 × 10 × 5 [g = 10 m/s², given]

W = 2000 joules

→ Power, P = work done /time

P = 2000/4

P = 500 joule/sec

The correct answer is option 2 i.e. Gravitational force.

• All objects in the universe attract each other. This force of attraction between objects is called the gravitational force.
• The attractive or repulsive forces between particles or objects due to their electric charges is known as electrostatic force.
• The force resulting due to the action of muscles is known as the muscular force; since it can be applied only when it is in contact with an object, it is also called a contact force.
• The force of attraction or repulsion that arises between electrically charged particles because of their motion is known as a magnetic force.

The correct answer is 3 ms^-1 and 4500 N.

Key Points

The initial velocity of the truck, u =0 ms^-1

The time taken by car, t = 30 s

Distance covered by the car, s = 1350 m

According to second law of motion,

s = ut + 1/2 (at²)

Put the values,

1350 = 0 x 30 + 1/2 (a x 900)

1350 = 450a

a = 3 ms-2

Now, Force = mass x acceleration

Force = 1500 x 3 = 4500 N