Question

A block of mass 40kg resting on a horizontal surface just begins to slide when a horizontal force of 120N is appiled to it once the motion starts it can be maintained by a force of 80N determine the coefficient of static friction and kinetic friction ( g = 9.8 m/s 2​

Answer 1

☆Concept:

▪︎limiting friction: also called static friction.Acts on the object when there is tendency of relation motion between the surfaces.It is self adjustable.

▪︎kinetic friction: it only acts when there is motion between the surfaces.

its value remains constant.

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☆Formula:

$\boxed{\bf{\green{Static\;friction= \mu_{s}N}}}$

$\boxed{\bf{\green{Kinetic\;friction= \mu_{k}N}}}$

☆Solution:

》at limiting,the static friction will be almost equal to maximum $\ F_{ext}$.

$\rightarrow{120= \mu_{s}N}$...(N=mg)

$\rightarrow{120= \mu_{s}40×9.8}$

$\rightarrow{\bf{ \mu_{s} = 0.31}}$

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》after motion kinetic friction will acts.

》that can be balanced by 80N only,during which the object will be moving with constant velocity.

$\rightarrow{80= \mu_{k}N}$

$\rightarrow{80= \mu_{k}40×9.8}$

$\rightarrow{\bf{ \mu_{k} = 0.2}}$

××××××--------×××××××--------×××××××

♧hope it helps!♧