# If an object is moving at 20 m/s over a surface with a kinetic friction coefficient of u_k=3/g, how much time will it take for the object to stop moving?

Feb 10, 2016

$t = 20 s$

#### Explanation:

${F}_{f} = k \cdot m \cdot g$
${F}_{f} = \frac{3}{\cancel{g}} \cdot m \cdot \cancel{g}$
${F}_{f} = m$
$F = m \cdot a \text{ The Newton's law}$
$m = m \cdot a$
$a = 1 \frac{m}{s} ^ 2$
${v}_{l} : \text{last velocity ; "v_i:" initial velocity}$
${v}_{l} = {v}_{i} - a \cdot t$
${v}_{l} = 0 \text{ when object is stops}$
$0 = 20 - 1 \cdot t$
$t = 20 s$