Test: Force & Pressure - 3 - Class 8 MCQ

The frictional force is a contact.
These are the forces that act upon bodies when they are in physical contact with each other and one body is trying to slide over the other body.

Magnetic force is a force, like gravity, that is able to act across a distance without touching an object that is attracted by it. So magnetic force is a non-contact force.

We know that pressure is defined as force acting normally per unit area of a surface.
It is given by
Pressure = Forece/Area = F/A

The correct calculation for the pressure exerted by the wooden piece should be considered.
Pressure is defined as force per unit area.
The wooden piece has a weight (force) of 5 N and lies on a face with dimensions 5 cm x 2 cm, giving an area of 5 × 2 = 10 cm². Therefore, the pressure exerted by the wooden piece is calculated as 5 N / 10 cm² = 0.5 N/cm². The correct answer is option 3, which is 0.5.

Friction opposes the relative motion between two surfaces in contact. Fluid friction can be minimized by giving suitable shapes to bodies moving in fluids. A car with a streamlined body suffers less air friction while moving and a car with a flat face will suffer higher air friction. As a result car with a streamlined body will require less force from the engine to maintain the same speed.

Old NCERT

• Statement 1 is incorrect: Pressure is defined as force per unit area, meaning it is directly proportional to the force applied and inversely proportional to the area over which it is applied.
• Statement 2 is correct: The moment arm is indeed the perpendicular distance from the pivot point to the line of action of the force, crucial in calculating torque.
• Statement 3 is misleading: Wooden sleepers help distribute weight, reducing pressure on the tracks, not necessarily increasing pressure.
• Statement 4 is incorrect: Pressure can be affected by surface roughness, as it can influence the contact area and force distribution.

Old NCERT

We know that Pressure = thrust/area
The weight of vehicle with narrow tyre and the one with wide tyre is the same. That means the thrust is equal in both cases. But we can change the effect of this thrust by changing the area on which it acts. The vehicle sinks into soft ground when the pressure is more, i.e the area is less.
 To decrease the pressure, wider tyres must have been used. This increases the area on which thrust acts. So that the vehicle does't sink into the soft ground.

Old NCERT

The rise of water in the dropper is due to atmospheric pressure.
When the bulb of a dropper is pressed, the pressure inside the dropper decreases and this causes the water to go inside the dropper.

When forces are applied inn the opposite directions, the forces get subtracted.
So, net force on the body = (5-2)N = 3N

The pressure at a point in the fluid is due to the weight of the fluid above that point, acting on unit area.
Since the weight above the bottommost point is the highest, the pressure is maximum at that point.

A fluid is defined as a substance that has no fixed shape and yields easily to external pressure. They are free to flow, and hence the name fluid. They are of two kinds- Gases and Liquids.

Solids are not classified as fluids as they have a definite shape and volume.

Old NCERT

A fluid is defined as a substance that has no fixed shape and yields easily to external pressure. They are of two kinds- Gases and Liquids.
The fluid pressure is, thus, of two kinds.
One is due to gases(air) and is called air pressure.
The other is due to liquids(water) and is called water pressure.

Old NCERT

The pressure is defined as the force per unit area. i.e  P=F/A
So the pressure depends on the force F and area A of contact.
If force is constant, the pressure is only depends on the area. 
A sharp knife edge has small area of contact and less area of contact will produce the more pressure. 
Thus, the option B can be correct.  

Old NCERT

Pressure is defined as P = Force applied/Area

So the pressure applied is inversely proportional to the area to which it is applied.

Since in a sharp needle, surface area on which the force is applied, is less than that for a blunt needle.

Hence, pressure exerted by a sharp needle is more than blunt needle. 

Force is an effort that comes into use to Change the state of motion or state of rest of the body.