# An object with a mass of 4 kg is lying still on a surface and is compressing a horizontal spring by 7/8 m. If the spring's constant is 16 (kg)/s^2, what is the minimum value of the surface's coefficient of static friction?

Apr 28, 2016

$0.36$

#### Explanation:

The spring applies a force of $- k x = - 16 \times \frac{7}{8} N = - 14 N$

Now the force of friction on the object = $\mu m g = \mu 4 \times 9.8 N$

so, if it is not moving, net force on the body must be zero,

hence:

$\mu 4 \times 9.8 = 14$
$\implies \mu = \frac{7}{19.6} \approx 0.36$