A block of mass 5 kg is (i) pushed in case (A) and (ii) pulled in… | JEE Main 2019 (12 Apr, Shift 2)

Q23JEE Main 2019 · 12 APR · SHIFT 2Medium

Friction Basics

A block of mass 5 kg is (i) pushed in case (A) and (ii) pulled in case (B), by a force F = 20 N, making an angle of 30° with the horizontal, as shown in the figures. The coefficient of friction between the block and floor is $\mu$ = 0.2. The difference between the accelerations of the blocks, in case (B) and case (A) will be: (g = 10 ms–2)

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Answer: (b)

Horizontal component in both cases: $F\cos 30^\circ = 10\sqrt{3} \approx 17.32$ N; vertical component $F\sin 30^\circ = 10$ N.
Push (A): $N = 50 + 10 = 60$ N, $f = 12$ N, $a_A = \dfrac{17.32 - 12}{5} = 1.064\text{ m/s}^2$
Pull (B): $N = 50 - 10 = 40$ N, $f = 8$ N, $a_B = \dfrac{17.32 - 8}{5} = 1.864\text{ m/s}^2$
$a_B - a_A = \dfrac{12 - 8}{5} = 0.8\text{ m s}^{-2}$ , so the answer is (b).

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