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So , here we have door which can get closed on its own due to spring. Agenda of Q is to put sth beside the door so that the door does not close .

The Q tells us that when we put a brick of 0.5kg. Door is able push the block. But if I keep a plank of mass 20g if which touches the door and the planks end touches the walls. The door remains closed. FRICTION is present

My solution to why does the door is able to push the block is because F=M*a. So , as the force becomes large due to acceleration of the door. The block is not able to apply enough counterattacking force on the door at that time and then kinetic friction happens due to it.

In case of plank , since it touches the door even before the plank moves. Therefore , acc of plank=0 and F by plank is also 0.

If my solution is correct , then why does in the case of a plastic bag or rod which is long and is touch the door and the wall same as plank. Then , why does the plastic gets deformed even though F of door is 0.

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    $\begingroup$ This question is hard to follow without images or diagrams of some sort. There also appears to be some missing information, e.g. why does a plastic bag suddenly appear in the last paragraph? $\endgroup$ – hazzey May 14 at 13:20
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    $\begingroup$ "But if I keep a plank of mass 20g if which touches the door and the planks end touches the walls. The door remains closed. FRICTION is present." No, you have wedged the door closed. This is nothing to do with friction. $\endgroup$ – Transistor May 14 at 16:17
  • $\begingroup$ Ok. I will update the question and post a picture as well. $\endgroup$ – Srijan M.T May 14 at 16:25
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    $\begingroup$ Adding a space before the full-stop at the end of the first paragraph does not improve the question enough to have it reopened. (It's also incorrect punctuation.) It's still not clear what the question is asking. $\endgroup$ – Transistor Jul 9 at 17:18