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A girl press her physics text book again...

A girl press her physics text book against a rough vertical wall with her hand. The direction of the frictional force on the book exerted by the wall is

A

downwards

B

upwards

C

out from the wall

D

into the wall

Text Solution

Verified by Experts

The correct Answer is:
B
Friction forces are always parallel to the surfaces in contact, while in this case, are the wall and the cover of the book. This tells us that the friction force is either upwards or downwards. Because the tendency of the book is to fall due to gravity, the friction force must in the upward direction.
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Knowledge Check

  • 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
    `muF` upwards where `mu` is the coefficient of static friction
    C
    mg and upwards
    D
    Equal and opposite to the resultant of F and mg

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    `mu Mg`
    B
    `M g`
    C
    `(Mg )/(mu)`
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    C
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