Question

Block $A$ weighs $4N$ and blocks weight $8N$. The coefficient of kinetic friction is $0.25$ for all surfaces. Find the force $F$ to slide $B$ at a constant speed when (a) $A$ rests on $B$ and moves with it, (b) $A$ is held at rest, and (c) $A$ and $B$ are connected by a light cord passing over a smooth pulley as shown in figure. respectively.

Answer 1

R.E.F image

(a) FBD of B

$F=\mu R$

$=\mu 12$

$=3N$

(b) FBD of B

$\sum y=0$

$\Rightarrow R=12N$

$F+4\mu =12M$

$\Rightarrow F=8\mu$

$=2N$

(c) T FBD

$T=4\mu$

$\sum y=0\Rightarrow R=12N$

$\sum x=0\Rightarrow T\mu R=FTAu$

$\Rightarrow F=12\mu$

$=3N$