Class 8 Science Chapter 11 MCQ

All are the examples of muscular force except one. An apple falling from a tree is example of gravitational force. The force with which the earth pulls the objects towards it, is called the force of gravity. Gravity is a natural force of attraction or pull.

Magnitude of force applied by A is greater than that of B because the block moves towards right i.e., towards B.

All are the examples of gravity force except one. A boy pushing a cart on a level plane is an example of contact forces. Remember, forces are used in our everyday actions like pulling, pushing, lifting, stretching, pressing and so on.

A dropper works on the existence of atmospheric pressure. When we press the rubber bulb of the dropper by keeping its nozzle dipped in water or liquid, the air present in the glass tube and bulb is seen to escape in the form of bubbles. Due to this, the air pressure inside the glass tube and rubber bulb of dropper is very much reduced. When we now released the rubber bulb of dropper, the much greater atmospheric pressure acting on the surface of liquid, pushes the liquid up into the dropper tube.

The electrostatic force is responsible for it, since on comparing the hair, the comb and hair get oppositely charged.

Which of the following are contact forces? [A] Friction and Gravitational force [B] Gravitational force and Magnetic force [C] Friction and Muscular force [D] Gravitational force and Muscular force

Force of friction is a contact force. It always acts when the bodies are in contact. A force which can be exerted by an object on another object only through “physical touching” is called a contact force. Such as: i)Muscular force and ii)Friction force

The force with which the earth pulls the objects towards it, is called the force of gravity. Gravity is a natural force of attraction or pull. If we drop a stone from some height, it falls down towards the earth. A leaf falls from the tree due to gravity. Rain falls down to earth due to the force of gravity. When we open a tap, water begins to flow down towards the ground due to the force of gravity. There are so many examples of gravitational force.

Pressure will be maximum in position V, because area of contact is minimum in this case and area is inversely proportional to pressure.

The force “F” is all the same in all situation making it constant. Using the formula: Pressure=Force/area. This suggest that since “F” is constant, decrease in area will lead to increase in pressure and vice vasa. This may be represented by a real-life example with a sharp healed shoe of a lady and a normal shoe. If a lady weighing 140N may step on you while wearing the sharp healed shoe, the pain will be more severe than while wearing a normal flat shoe. Therefore, the lesser the area, the greater the pressure. Hence, your answer will be 10 m2, option [C].

Atmospheric pressure is the pressure exerted by the atmosphere, or rather the weight of air above a point on Earth. It can be measured using a barometer. The unit of pressure is Pascals. As we go to a higher altitude on Earth, the weight of air above it decreases, so the pressure will also be lesser. So atmospheric pressure decreases with increasing elevation. Atmospheric pressure is measured using a barometer. At sea level, the barometer will read a value of standard or normal atmospheric pressure, equivalent to the pressure exerted by 760 mm or 76 cm, tall column of mercury or 101.3 kilopascals. Hence, your answer will be option [C].

Here, all the statements are correct. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

A force which can be exerted by an object on another object only through “physical touching” is called a contact force. Such as: i)Muscular force and ii)Friction force These are example of contact forces, but a force which can be exerted by an object on another object even from a distance (without touching) is called a non-contact force. Such as, i)Magnetic force ii)Electrostatic force and iii)Gravitational force

Force = 100 N, Area = 3 m2 Putting these values in the formula for pressure: Pressure = 100 N/2 m2 = 50 N/m2 Thus, the pressure is 50 newtons per square meter or 50 pascals.

The English scientist Isaac Newton had given the idea for gravitational force when he saw an apple fall from a tree. The force with which the earth pulls the objects towards it, is called the force of gravity. Gravity is a natural force of attraction. We are all pulled (including every object) to the earth by the force of gravity.

Liquids exert pressure on every direction based on the kinetic energy of their molecules. Now, in case of mustard oil the pressure exerted will not be much due to low kinetic energy of its molecules, while take the example of cold drinks after getting shaked on the other side, the molecules exert so much pressure its almost like it, flood out of the container.

We can calculate pressure using the formula, Pressure = Force / Area. In this case, pressure = 10 kPa = 10 x 1000 = 10000 Pa and area = 0.3 m2. So, we can find force as follows: Force = Pressure x area = 10000 x 0.3 = 3000 Newtons. So, a force of 3000 N is required to create a pressure of 10 kPa for an object of area 0.3 m2.

A school bag or shoulder bag has wide strap made of thick cloth (canvas) so that the weight of bag may fall over a large area of the shoulder of the child producing less pressure on the shoulder. And due to less pressure, it is more comfortable to carry the heavy school bag.

The SI unit of pressure is pascal (Pa) but atmospheric pressure is usually measured in the unit of “millimeter of mercury” (mm of mercury) for the sake of convenience in measuring it.

Here, all the statements are correct. Hence, your answer will be option [D].

The pressure depends on two factors: a) Force applied and b) Area over which force acts. Pressure = Force / Area Area = Pressure / Force = 500/ 5 = 100 cm2