Question

A force of $100N$ is required to set in motion a $25kg$ block resting on a horizontal surface. Once the body is set in motion, a horizontal force of $665N$ just keeps the block moving with uniform speed. Find ${\mu }_s$ and ${\mu }_k$

Answer 1

In case of static friction we have

$F={\mu }_{s}mg$

$100={\mu }_s\times 25\times 10$

${\mu }_s=0.4$

Thus static friction is $0.4$.

Now a force of $65N$ is used to move the body with uniform speed.

Then

$65={\mu }_{k}mg$

$65={\mu }_k\times 25\times 10$

${\mu }_k=0.26$

Thus kinetic friction is $0.26$.