JEE Main 2026 · 4 Apr · Shift 1 · Physics Q28

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The time taken by a block of mass $m$ to slide down from the highest point to the lowest point on a rough inclined plane is 50 % more compared to the time taken by the same block on identical inclined smooth plane. Both inclined planes are at 45° with the horizontal. The coefficient of kinetic friction between the rough inclined surface and block is ________.

3/4

2/3

5/9

4/9

Answer and worked solution

Official answer: C

Same distance from rest, so $t\propto a^{-1/2}$ . $t_r=1.5t_s$ means $a_s=2.25a_r$ .

At 45°. $a_r=g\sin45^\circ(1-\mu)$ , so $\frac1{1-\mu}=\frac94$ and $\mu=\frac59$ .

(C)

Topics:Friction Motion in a straight line

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JEE Main 2026 · 4 Apr · Shift 1, Physics question 28