# If an object with a mass of 10 kg  is moving on a surface at 8 m/s and slows to a halt after  7 s, what is the friction coefficient of the surface?

initial vel = $u = 8 \frac{m}{s}$
final vel =$v = 0$
retardation =a =?
time $t = 7 s$
$0 = u - a \times t$
$0 = 8 - a \times 7$
$a = \frac{8}{7} \frac{m}{s} ^ 2$
Now $\mu m g = m \times a$
$\mu = \frac{a}{g} = \frac{8}{7} \times \frac{1}{9.8} = 0.117$