Spring fitted doors close by themselves when released. You want t… - Vidyadip

Question

Spring fitted doors close by themselves when released. You want to keep the door open for a long time, say for an hour. If you put a half kg stone in front of the open door, it does not help. The stone slides with the door and the door gets closed. However, if you sandwitch a 20g piece of wood in the small gap between the door and the floor, the door stays open. Explain why a much lighter piece of wood is able to keep the door open while the heavy stone fails.

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Answer

In the initial case normal is equal to weight of body but in the second case as body is pressed so normal increases hence more normal more will be frictional force.

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