Force Test - 1

The friction of a surface is increased by increasing its roughness. The roughness of a carom board does not increase when it is powdered. Hence, the friction of a carom board surface does not increase when it is powdered.

The force exerted from a distance is called non-contact force. Muscular force is not exerted from a distance. Hence, it is not a non-contact force.

The correct answer is B.

Why alternatives A, C and D are incorrect :

Magnetic force, electrostatic force, and gravitational force all act from a distance. These are called non-contact forces.

Sole of shoes are treaded so as to increase the rate of frictional force between the shoe and the ground. This helps the wearer to have a better grip on the ground.

The size of an elastic object is changed by the application of forces from opposite directions. A catapult consists of two rubber bands. Rubber is an elastic material. Its shape changes on stretching. Hence, the stretching of the strings of a catapult involves a change in its size.

Static friction is the measure of the minimum force required to overcome the interlocking between two surfaces in contact, to move one over the other.

Lubricants are thick liquids that make rough surfaces smooth and slippery. The application of lubricants reduces the friction between two surfaces moving relative to each other. Since the use of lubricants between two surfaces reduces the value of X, X must be the force of friction.

Friction is caused due to the irregularities that are present between the surfaces of two bodies when the surfaces are in contact with each other.

The bar magnet exerts magnetic field that causes iron fillings to get attracted toward it. Hence, iron filings get attracted toward a bar magnet because of the presence of magnetic force.

The correct answer is C.

Why alternative A is wrong:

Gravitational force is a phenomenon through which all objects tend to attract each other, but this force is not significant enough so as to draw iron fillings toward a bar magnet. Hence, this alternative is incorrect.

Why alternative B is wrong:

Friction can be defined as the resistance hindering the relative movement, or the propensity toward such a movement, of two surfaces that are in contact. Hence, this alternative is incorrect.

Why alternative D is wrong:

Neither the bar magnet nor the iron filings are supplied with any kind of electric current. Thus, electric force cannot be the reason for the attraction of the iron filings to the magnet. Hence, this alternative is incorrect.