$$a = \frac{20}{5} = 4$$ m/s²
$$10 = \mu \times 5 \times 9.8$$
$$20 = 0 + a \times 5$$
$$\mu = \frac{10}{5 \times 9.8} = 0.2$$
Using the equation: $$f = \mu N$$, where $\mu$ is the coefficient of friction and $N$ is the normal reaction. m karim physics numerical book solution class 11