JEE Main · 2025 · 07 Apr 2025 · Shift 1 · Laws of Motion

A cubic block of mass

m

is sliding down on an inclined plane at

6 0^{\circ}

with an acceleration of

\frac{g}{2}

, the value of coefficient of kinetic friction is

(A) $3 - 1$ ✓ Correct
(B) $\frac{3}{2}$
(C) $\frac{2}{3}$
(D) $1 - \frac{3}{2}$

Answer: (A)

Solution

Taking down the incline as positive, gravity drives the block while kinetic friction opposes it:

m g sin 6 0^{\circ} - μ m g cos 6 0^{\circ} = ma .

With

a = \frac{g}{2}

, dividing through by

m g

sin 6 0^{\circ} - μ cos 6 0^{\circ} = \frac{1}{2}, \frac{3}{2} - \frac{μ}{2} = \frac{1}{2} .

Solving for the coefficient,

μ = 3 - 1.

The coefficient of kinetic friction is

3 - 1

JEE Main · 2025 · 07 Apr 2025 · Shift 1 · Single correct option

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