Question

Three blocks $A,B$ and $C$ of masses $4kg,2kg$ and $1kg$ respectively, are in contact on a frictionless surface, as shown in the figure. If a force of $14N$ is applied on the $4kg$ 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,
$m_A=4kg$
$m_B=2kg,m_C=1kg$
and $F=14N$

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

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