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4-2.Friction
medium
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........ $N$ . $(g = 10\, m/s^2)$
A
$900$
B
$200$
C
$1100$
D
$700$
Solution
Friction between block $A$ and block $B$ and between block $\mathrm{B}$ and surface will oppose the
$F$
$\therefore \mathrm{F}=\mathrm{F}_{\mathrm{AB}}+\mathrm{F}_{\mathrm{BS}}$
$=\mu_{\mathrm{AB}} \mathrm{m}_{\mathrm{A}} \mathrm{g}+\mu_{\mathrm{BS}}\left(\mathrm{m}_{\mathrm{A}}+\mathrm{m}_{\mathrm{B}}\right) \mathrm{g}$
${=0.2 \times 100 \times 10+0.3(100+200) 10}$
${=200+900=1100 \mathrm{N}}$
Standard 11
Physics
