Question

A wooden box of mass 60 kg is at rest at horizontal surface of platform. A coolie requires a force of 78.4 N to just slide. Once the motion begin force of 39.4N is sufficient to keep box moving with uniform velocity.
Calculate the coefficient of static and kinetic friction.
(g = 9.8 $m/s^2$)

Answer 1

Force required to just slide the object $F_{applied}=78.4N$

Static friction $F_s=F_{applied}$

Or ${\mu }_{s}mg=78.4$

Or ${\mu }_s\times 60\times 9.8=78.4$

$⟹{\mu }_s=0.133$

Kinetic friction :

Force required after sliding begins $F=39.4N$

Static friction $F_k=F$

Or ${\mu }_{k}mg=39.4$

Or ${\mu }_k\times 60\times 9.8=39.4$

$⟹{\mu }_k=0.067$