Q.3 Alida runs her toy car on a dry marble floor, wet marble floor, newspaper and towel spread on the floor. The force of friction acting on the car on different surfaces in increasing order will be
(a) wet marble floor, dry marble floor, newspaper and towel.
(b) newspaper, towel, dry marble floor, wet marble floor.
(c) towel, newspaper, dry marble floor, wet marble floor.
(d) wet marble floor, dry marble floor, towel, newspaper.


Answer :

Alida runs her toy car on a dry marble floor, wet marble floor, newspaper and towel spread on the floor. The force of friction acting on the car on different surfaces in increasing order will be

(a) wet marble floor, dry marble floor, newspaper and towel.

EXPLANATION

The force of friction will be less in marble floor as compared to the newspaper and the towel because the marble has very less roughness as compared to the other two things.

Now between dry marble and wet marble, wet marble will have the lowest force of friction because it has negligible roughness or no roughness. This is because the water spread on wet marble acts as a lubricant and fills the roughness present on the surface of the marble, thus making it more smooth and slippery. As a result, when the toy car moves on the wet marble, there is no interlocking between the wet marble surface and the toy car's wheel surface. Thus there is no friction acting between the two and the toy car slips easily on the wet marble surface.

Now between dry marble and newspaper, dry marble has less roughness and thus less interlocking takes place between the dry marble surface and the toy car's wheel surface, resulting in the easy movement of the toy car on the dry marble as compared to the newspaper.

Now between newspaper and towel, newspaper has less roughness, thus there is less interlocking between the newspaper surface and the toy car's wheel surface, as a result toy car moves easily on newspaper as compared to the towel.

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