00:01
Hello students this question is about static friction friction is an opposing force we know it opposes the motion of an object static friction acts on an object which is at rest question is to find whether the work done by the static friction is positive negative or zero it is considered all possible cases first consider an object to be addressed since there is no force acting on this block a, the applied force is zero.
00:37
Hence, static friction is also zero.
00:41
Thus, we can say that the work done by the static friction is zero in this case.
00:49
Now let us assume second case where an object is in motion.
00:55
Let the block a be moving towards right by means of an applied force faa.
01:00
Since it is moving towards right, there exists frictional force that opposes its motion towards lift.
01:08
We know the formula of work done, which is force into distance into cost of angle between them, cost theta, fs cost data.
01:17
Thus, in this case, work couldn't by the static friction will be f into s into cost of 180 degrees.
01:27
As the block is moving towards right and static friction acts towards left.
01:31
There exists an angle 180 degree between them.
01:34
Hence, we say that work done with static friction is negative.
01:40
As per our assumption, in this case work done is negative.
01:43
Finally, let us assume motion of two blocks together.
01:51
When two blocks that are kept one above the other, here block b is kept over block a...