Two blocks (P and Q) with respectively masses 2 kg and 1.5 kg are joined by a massless thread. These blocks are mounted on a frictionless pully which is fixed on the edge of a cube (S), as shown in the figure below. Block P is positioned on the top surface which has no friction and block Q is in contact with side-surface, having coefficient friction μ. The cube (S) moves towards the right with acceleration of 2g, where g is gravitational acceleration. During this movement the block P and Q remain stationary. The value of μ is ______. (take g=10m/s2)
(A)0.33
(B)0.67✓ Correct
(C)1
(D)0.5
Answer: (B)
Solution
Working in the cube's frame, each block feels a pseudo-force opposite to the cube's acceleration g/2. Block P on the smooth top is held only by the thread, so the tension carries it along: T=mP⋅2g=2×5=10 N. Block Q presses on the vertical side, where the face supplies the horizontal normal force that accelerates it: N=mQ⋅2g=1.5×5=7.5 N. Vertically Q is in balance under its weight, the tension and friction: f=mQg−T=1.5×10−10=5 N. At the limiting condition f=μN, so μ=Nf=7.55. The coefficient of friction is μ≈0.67.
JEE Main · 2026 · 06 Apr 2026 · Shift 1 · Single correct option
