Block A of mass 4 kg is placed on the rough surface of a long block B of mass 6 kg. Block B is placed on smooth horizontal surface. Blocks are given the velocities as shown in figure. List-I List-II (

Question

Block A of mass 4 kg is placed on the rough surface of a long block B of mass 6 kg. Block B is placed on smooth horizontal surface. Blocks are given the velocities as shown in figure.

blocks with velocities

List-I	List-II
(P) Common velocity (in m/s) of blocks when sliding between A and B stops.	(1) 108
(Q) Velocity (in m/s) of centre of mass at shown moment.	(2) 80
(R) Magnitude of work done (in joule) by friction on B.	(3) 78
(S) Magnitude of net work done (in joule) by friction.	(4) 30
-	(5) 8

TestHub · Accepted Answer

Common velocity: ( 4 + 6 ) v 0 ​ = 4 ( 5 ) + 6 ( 10 ) ⇒ v 0 ​ = 8 m/s - P → 5 . Centre of mass velocity is the same 8 m/s - Q → 5 . Work by friction on B: 2 1 ​ ( 6 ) 8 2 − 2 1 ​ ( 6 ) 1 0 2 = − 108 J , magnitude 108 - R → 1 . On A: 2 1 ​ ( 4 ) 8 2 − 2 1 ​ ( 4 ) 5 2 = 78 J ; net = − 108 + 78 = − 30 J , magnitude 30 - S → 4 . Hence option (A).

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