A block of weight rests on a horizontal surface for which the coefficients of…

PHYSICS · Single correct · CBSE · Physics · Laws of Motion · Laws of Motion

Problem

A block of weight

40\,\text{N}

rests on a horizontal surface for which the coefficients of friction are

\mu_s=0.30

and

\mu_k=0.225

. A horizontal force is slowly increased from

0

20\,\text{N}

while the block’s motion is monitored. Which of the following descriptions best matches the resulting graph of friction force magnitude versus applied force magnitude? (a) The friction force increases linearly with

F_{\text{app}}

up to

9\,\text{N}

, then remains constant at

9\,\text{N}

F_{\text{app}}

continues to increase. (b) The friction force increases linearly with

F_{\text{app}}

up to

12\,\text{N}

, then drops suddenly to

9\,\text{N}

and remains constant as

F_{\text{app}}

continues to rise. (c) The friction force increases linearly with

F_{\text{app}}

up to

12\,\text{N}

, then remains constant at

12\,\text{N}

even as

F_{\text{app}}

rises to

20\,\text{N}

. (d) The friction force stays at zero until

F_{\text{app}}

equals

12\,\text{N}

, then jumps to

12\,\text{N}

and follows

F_{\text{app}}

exactly for larger values.

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