A mass of 1 kg is kept on an inclined plane with 30° inclination with… | JEE Main 2026 (5 Apr, Shift 2)

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Work by a Constant Force

A mass of 1 kg is kept on an inclined plane with $30^\circ$ inclination with respect to horizontal plane and it is at rest initially. Then the whole assembly is moved up with constant velocity of $4\text{ m/s}$ . The work done by the frictional force in time 2 s is ______ J. (Take $g = 10\text{ m/s}^2$ )

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Answer: (a)

Block stays at rest on the incline, so static friction balances $mg\sin 30^\circ$ : $f = 1 \times 10 \times \frac{1}{2} = 5$ N, directed up the incline.
The assembly moves vertically up by $s = vt = 4 \times 2 = 8$ m.
Friction makes angle $60^\circ$ with the vertical, so its vertical component is $f\sin 30^\circ = 2.5$ N.
$W_f = 2.5 \times 8 = 20$ J
So the answer is (a) 20.

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