Block A of mass m rests on the plank B of mass 3 m which is free to slide on - Physics - Communication Systems

Question

Block A of mass m rests on the plank B of mass 3 m which is free to
slide on a frictionless horizontal surface The coefficient of
friction between the block and plank is 0 2 If a horizontal force
of magnitude 2 mg is applied to the plank B, the acceleration of A
relative to the plank and relative to the ground respectively
are:

(1) 0 , g 2 (2) 0 , 2 g 3 (3) 3 g 5 ,   g 5 (4) 2 g 5 ,  
g 5

Shobhit Mittal · Accepted Answer

Dear Student,

let both the plank and the block move togetherthen accn of the system a=2mg4m=g/2pseudo force on A=ma=mg2maximum friction force =0
2mgsince pseudo force is greater then the mximum friction force body will slip on plank 
accn of the A wrt ground a=0 2mgm=0
2g=g5accn of plank a'=2mg-0 2mg3m=0
6g accn of the A wrt  Ba''=0
6g-0 2g=0 4g=2g5option 4REgards