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(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.

- Q.1 Fill in the blanks. (a) Friction opposes the ______ between the surfaces in contact with each other. (b) Friction depends on the ______ of surfaces. (c) Friction produces ______ (d) The sprinkling of powder on the carrom board _______ friction. (e) Sliding friction is _______ than the static friction.
- Q.2 Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below. Choose the correct arrangement. (a) rolling, static, sliding (b) rolling, sliding, static (c) static, sliding, rolling (d) sliding, static, rolling
- Q.4 Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of frictional force acting on it.
- Q.5 You spill a bucket of soapy water on a marble floor accidentally. Would it make it easier or more difficult for you to walk on the floor? Why?
- Q.6 Explain why sportsmen use shoes with spikes.
- Q.7 Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?
- Q.8 Explain why sliding friction is less than static friction.
- Q.9 Give examples to show that friction is both a friend and a foe.
- Q.10 Explain why objects moving in fluids must have special shapes.

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