in high school , i solve friction questions by making FBD but recently i got a doubt while imagining a situation
suppose there is a block of mass 4kg kept on ground and we apply a force of 20N and lets assume the limiting friction is 14N and kinetic friction is 12N , so the block will start sliding and when we make equation of motion for this block we will get
20N – 12N = 4a
a = 2m/s²
so the block will have acceleration 2m/s²
but if we think of what will happen after our force, the block will stop after sometime
so what does actually happen after this 2m/s² acceleration which causes the block to stop , it will be friction obviously ( if we neglect air resistance ) but does friction keep resisting the motion of block and if yes then can anyone explain thoroughly what exactly happens cause this was never taught in our class ,
thanks
In: Physics
Let’s say that you push for one second, then let go. The moment you let go, the block has a velocity of 2 m/s. Now, instead of a net force of 8N acting in the direction of its travel, you have only 12N of friction acting in the opposite direction.
That means the block is now accelerating in the opposite direction at 3 m/s² and reaching a velocity of 0 after 2/3 s.
The interaction between block and surface “doesn’t care” whether the block is pushed such that it accelerates (F > 12N in your example) , stays at a constant speed (F=12N) or slows down (F< 12N). As long as the Block moves, it will exert a set force opposed to the direction of movement.
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