Work Power and Energy 3 Question 2
2. Statement I A block of mass $m$ starts moving on a rough horizontal surface with a velocity $v$. It stops due to friction between the block and the surface after moving through a certain distance. The surface is now tilted to an angle of $30^{\circ}$ with the horizontal and the same block is made to go up on the surface with the same initial velocity $v$. The decrease in the mechanical energy in the second situation is smaller than that in the first situation.
Statement II The coefficient of friction between the block and the surface decreases with the increase in the angle of inclination.
(2007, 3M)
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Answer:
Correct Answer: 2. (c)
Solution:
- In statement I Decrease in mechanical energy in case I will be
$$ \Delta U _1=\frac{1}{2} m v^{2} $$
But decrease in mechanical energy in case II will be
$$ \begin{aligned} & \Delta U _2=\frac{1}{2} m v^{2}-m g h \\ \Rightarrow \quad & \Delta U _2<\Delta U _1 \end{aligned} $$
or statement I is correct.
In statement II Coefficient of friction will not change or this statement is wrong.
