Q95 of 100 Page 233

Explain why, it is easier to drag a mat on floor when nobody is sitting on it but much more difficult to drag the same mat when a person is sitting on it.

When no person is sitting on the mat, then the mat and floor are not pressed together.


Thus, there is no friction.


But, when a person is sitting on the mat.



Then due to the weight of the person, the mat and floor are pressed together harder, increasing the friction too much. Thus, then it is very difficult to drag the person.


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When a pencil cell is released from a certain point on an inclined wooden board, it travels a distance of 35 cm on floor A before it comes to rest. When the same pencil cell is released from the same point on the same inclined board, it travels a distance of 20 cm on floor B before coming to rest. Which floor, A or B, offers greater friction? Give reason for your answer.

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What kind of friction comes into play:

(a) when a block of wood kept on table moves slowly ?


(b) when a block of wood kept on table just tends to move (or slip)?


(c) when a block of wood kept on cylindrical iron rods moves?