Question

2. A 5-kg block is at rest on a horizontal surface. The coefficients of static and kinetic friction between the block and the surface are 0.40 and 0.30, respectively. a) What horizontal force must be applied to just start the block moving?

Answer 1

Given data:

Mass of the block;

$m=5\text{ kg}$

Coefficient of static friction;

$\mu_s=0.4$

The static friction is given as,

$f_s=\mu_smg$

Here, g is the acceleration due to gravity.

Substituting all known values,

$\begin{gathered} f_s=(0.4)\times(5\text{ kg})\times(9.8\text{ m/s}^2) \\ =19.6\text{ N} \end{gathered}$

In order to just move to block the applied force must be greater or equal to the static friction force. Therefore, a 19.6 N of horizontal force must be applied to just start the block moving.