Class 8 Science Chapter 8 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.

It will be magnetic force because as electric current flows through the coil, it behaves like electromagnet and magnetic force is created.

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 reason for repulsion may be either an electrostatic (in case of similar charges) or a magnetic (in case of similar poles) force.

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

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

An electrostatic precipitator is a type of filter (dry scrubber) that uses static electricity to remove soot and ash from exhaust fumes before they exit the smokestacks. This one common air pollution control device. Most power stations burn fossil fuels such as coal or oil to generate electricity for use.

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

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].

A force can change the speed of a moving object. A force can change the direction of a moving object. A force can change the composition of a moving object. A force can change the shape and size of an object. But when a batsman hits a moving cricket ball, its direction and speed changed, not shape and size. Hence, your answer will be option [D].

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

A force can change the speed of a moving object. A force can change the direction of a moving object. A force can change the composition of a moving object. A force can change the shape and size of an object. But force cannot change the composition of a moving object or any object. Though composition is a chemical change.

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

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.

On the surface of earth, the atmospheric pressure is maximum at the sea level, because the column of air above us is tallest at the sea level. The atmospheric pressure on the surface of earth (at the sea-level) is 101.3 kilopascals, which is equivalent to the weight of 10 elephants pressing on each square metre area. As we go up in the atmosphere from the surface of earth, the atmospheric pressure goes on decreasing.

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 blunt knife does not cut an object easily because due to its thicker edge, the force of our hand falls over a larger area of the object and produces lesser pressure. This lesser pressure cuts the object with difficulty.

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.

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

When we press the rubber sucker on a flat, smooth surface, its concave rubber cup gets flattened to a large extent, pushing out most of the air from beneath it. Since, very little air remains inside the flattened rubber sucker, therefore, the air pressure inside the rubber sucker becomes very low (and a partial vacuum is created). The much greater atmospheric pressure acting on the rubber sucker from outside fixes the rubber sucker firmly on the flat surface.