Explanation

(a) [image:5_image218.jpeg]
From equation of motion
$v^{2} = u^{2} - 2as$
Where $v$ is final velocity, $u$ the initial velocity, $a$ acceleration and $s$ the displacement.
Given, $\ v = 0,u = 20\ {ms}^{- 1},\ s = 40\ m$
$\therefore\ \ \ 0 = (20)^{2} - 2 \times 40 \times a$
$\Longrightarrow \ \ a = 5\ {ms}^{- 2}$
Kinetic (or dynamic) friction occurs when two objects are moving relative to each other and rub together. It is given by
$\mu_{x} = \frac{a}{g} = \frac{5}{10} = 0.5\ $