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.

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.

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

As we know that pressure exerted by the body is inversely proportional to the area where force is applied. So, which has less area of cross section in contact with the surface will exert more pressure on the ground. It is clear that height from the base exerts more pressure. Therefore, the maximum pressure is exerted when length and height form the base.

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].

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].

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

The rise in the level of mercury in glass tube of thermometer will not work due to the presence of atmospheric pressure. A thermometer works on the principle that mercury expands with increase in temperature. So, the mercury in a glass tube of thermometer will rise only due to increase in temperature.

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

The strength of a force is expressed by its magnitude. The magnitude of force is expressed in the SI unit of force called “Newton”.

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.

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

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.

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.

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