Question

A block $ A $ of mass $ 100\, kg $ rests on another block $ B $ of mass $ 200\, kg $ and is tied to a wall as shown in the figure. The coefficient of friction between $ A $ and $ B $ is $ 0.2 $ and that between $ B $ and the ground is $ 0.3 $ . The minimum force $ F $ required to move the block $ B $ is $ (g = 10 \,ms^{−2}) $

• A. 900 N
• B. 200 N
• C. 1100 N
• D. 700 N

Answer 1

Answer: (C)

Friction force between block $A$ and block $B$ and between block $B$ and surface will oppose the $F$
$\therefore F=F_{A B}+F_{B S} $
$=\mu_{A B}\,m_{A}\, g+\mu_{B S}\left(m_{A}+m_{B}\right) g $
$=0.2 \times 100 \times 10+0.3(100+200) 10 $
$=200+900=1100\, N$
This is the required minimum force to move the block $B$.