A girl holds a book of mass $m$ against a vertical wall with a horizontal force $F$ using her finger, so that the book does not move. The frictional force on the book by the wall is
A$F$ and along the finger but pointing towards the girl
B$\mu F$ upwards, where $\mu$ is the coefficient of static friction
C$m g$ and upwards
Dequal and opposite to the resultant of $F$ and $m g$
KVPY 2012, Medium
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B$\mu F$ upwards, where $\mu$ is the coefficient of static friction
b (b)
Minimum force $F$ must be such that generated friction is able to balance weight $m g$ of book.
So, $\quad f=\mu N=\mu F$.
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