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Correct option is B) opposite

Total forces acting downwards = 2 N + 22 N = 24 N 

Total forces acting upwards = 8 N + 14 N = 22 N 

Resultant force = Difference between the magnitude of forces = 24 N – 22 N = 2 N . 

The wooden block will move in the downward direction with the resultant force of 2 N acting on it.

4. all of these

Fill in the blanks. 

1. Rolling friction is less than sliding friction.

 2. Smoother the surface, lesser is the frictional force offered by it. 

3. Friction depends upon the weight of an object. 

4. Friction is a type of contact force. 

5. Bicycles use ball bearings to reduce friction between the pedals and the crank

1. More the roughness of a surface, greater is the friction. 

2. Rolling friction offers less resistance than sliding friction. 

3. Weight remaining the same, friction is independent of area of surface in contact. 

4. The force of friction acting between two bodies in contact while at rest is known as static friction. 

5. Sliding friction and rolling friction are types of kinetic friction.

4. opposes motion

Sliding friction can be changed into rolling friction easily by providing wheels or ball bearings to the objects to reduce friction and facilitate easy movement.

It is because when the object is at rest, static friction occurs. The static friction is maximum when the applied force is just short of the force required to start motion between the two bodies in contact. Once the object starts moving, friction (resistance) we feel decreases.

While walking we apply force on the ground.

Muscular force.

When we roll an object on a surface, the friction produced between the object and the surface is called rolling friction. Example : when we pull our large suitcases on wheels, rolling friction comes into play. The wheels reduce friction and cut down a lot of effort required to move the suitcase (Rolling friction is less than sliding friction).

4. all of the these

Pressure = \(\cfrac{force}{area\,on\,which\,the\,force\,is\,applied}\)

∴ The unit of pressure = \(\cfrac{the\,unit\,of\,force}{the\,unit\,of\,area}\)

The SI unit of force is the newton (N) and that of area is m . Therefore, the SI unit of pressure is N/m² . It is called the pascal (Pa). 1 Pa = 1 N/m² . 

[Note: The unit pascal is named in honour of Blaise Pascal (1623-62), French mathematician, physicist and philosopher.]

A force that acts between two objects even if the two objects are not in contact, is called a non contact force. 

Example: The earth revolves around the Sun.

A force that acts through a direct contact of two objects or via one more object, is called a contact force. 

Example: If a ball at rest on the ground is kicked, it starts moving.

Porter place a round piece of cloth on their heads to increase the area of contact of the load with the head. So the pressure on their head is reduced and they can carry heavy load easily

At present, 23% of total electricity is generated in India using hydro-energy. 

Power = (Force x Distance)/Time

= (750 x 16)/5watt = 2400watt.

= 2.4kw.

Yes, since power = work/time the two agents can have different powers if they take different amounts of time to do the same work. 

Amount of work done is equal to zero. Work is said to be done only when there is displacement produced. In case of a body moving in a circular path, the body comes to its original place, therefore, there is no displacement and hence work is zero.

Work is said to be done if a body undergoes displacement due to applied force. Work done = Force × Displacement 

Work done is zero by the moon, as there is no displacement since it is moving in a circular path.

Earth exerts a force of attraction on each object. This force is due to gravity and its magnitude is directly proportional to the mass of the object. This force is known as gravitational force and its units are gravitational units. 

In MKS system the gravitational unit of force is kilogramme force i.e., kgf. In CGS system it is gramme force, gf. 

A bullet moving with high velocity has a large momentum. When it strikes the window pane, the velocity decreases and momentum reduces to a very small value. This sudden change in momentum exerts a large impulsive force enough to pierce through the window pane, making a hole. On the other hand, the velocity of a pebble thrown at it is not very high, its momentum is less. So. change in momentum (or force) is less which only make cracks in the window pane.

Work done, W = 1/2m(v₂² - v₁²)

= 1/20x 20(50² - 40²) = 9000J

The moon is revolving around the earth. In this process, the work done by the gravitational force is zero because the displacement of the moon is at right angle to the gravitational force.

When the bullet strikes the glass, the part of the glass coming in contact with the bullet, immediately shares the large velocity of the bullet and makes a hole in it while the rest of the glass pane, due to inertia of rest, remains at rest and so is not smashed. But when a stone strikes the same glass pan, the surrounding part of the glass gets time to share the comparatively low velocity of stone and so it is smashed.

The work done by the coolie is zero because there is no displacement of’ the load in the direction of force, which he is applying vertically upwards. 

We know w = Fdcosθ.

Since force is normal to displacement. so θ = 90°

Hence work done W = Fdcosθ    90 = 0.

Gravitational force.

Gravitational force.

Gravitational force.

 (i) Centre of gravity of a uniform ring is at its centre. (ii) False.

(i) At the centre of ring, (where there is no mass) 

(ii) False

(a) False (b) True

Magnetic force.

Centre of gravity is the point about which the algebraic sum of moments of weights of particles constituting the body is zero and the entire weight of the body is considered to act at this point.

The whole weight of body should act at that point.

The effect of force depends on two things 

1. The amount of force applied the more the force applied the greater the effect will be. 

2. The area on which the force is applied. The smaller the area, the force is applied on the greater the effect will be.

The magnitude of a non-contact force depends on distance of separation of two bodies. Magnitude of force decreases as the distance increases.

1. Magnitude of the force

2. The area over which it acts.

(i) False. The position of centre of gravity of a body of given mass depends on its shape i.e., on the distribution of mass in it.

(ii) True.

Yes, the centre of gravity can be situated outside the material of the body. For example, centre of gravity of ring.

The position of centre of gravity of a body of given mass depends on its shape i.e., on the distribution of mass in it. For example: the centre of gravity of a uniform wire is at its mid-point. But if this wire is bent into the form of a circle, its centre of gravity will then be at the centre of circle.

The position of centre of gravity of a 

(a) rectangular lamina is at the point of intersection of its diagonals.

(b) cylinder is at the mid point on the axis of cylinder.

4. has all the above disadvantages