Question

A block starts moving up a fixed inclined plane of inclination $\text{60}^{^\circ }$ with a velocity of $20 \, ms^{- 1}$ and stops after $\text{2 s}$ . The approximate value of the coefficient of friction is [ $g=10 \, ms^{- 2}$ ]

• A. $\text{3}$
• B. $\text{3} \text{.3}$
• C. $\text{0} \text{.27}$
• D. $\text{0} \text{.33}$

Answer 1

Answer: (C)

Retardation of the block is
$a=g\left(\text{sin} \theta + \mu cos \theta \right)=5\left(\sqrt{3} + \mu \right)$
$v=u-at=0\Rightarrow a=\frac{u}{t}\Rightarrow 5\left(\sqrt{3} + \mu \right)=\frac{20}{2}\Rightarrow \mu =0.27$