Question

Three blocks $A, B$ and $C$ of masses $4\, kg , 2\, kg$ and $1\, kg$ respectively, are in contact on a frictionless surface, as shown in the figure. If a force of $14\, N$ is applied on the $4\, kg$ block, then the contact force between $A$ and $B$ is

• A. 2 N
• B. 6 N
• C. 8 N
• D. 18 N

Answer 1

Answer: (B)

Given,
$m_{A}=4\, kg$
$m_{B}=2\, kg , m_{C}=1\, kg$
and $F=14\, N$

So, total mass, $M=4+2+1=7\, kg$
Now,
$F=M a \Rightarrow 14=7 a$
$\Rightarrow a=2\, ms ^{-2}$
FBD of block $A$,

Hence, the contact force between $A$ and $B$ is $6\, N$.