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4-2.Friction
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A block of mass $70\,kg$ is kept on a rough horizontal surface $(\mu = 0.4)$. A person is trying to pull the block by applying a horizontal force, but the block is not moving. The net contact force exerted by the surface on the block is $F$, then
A
$F = 700\,N$
B
$F = 280\,N$
C
$700\,N \le F \le 754\,N$
D
$F = 754\,N$
Solution
$\mathrm{N}=70 \mathrm{g}=700 \mathrm{N}$
$\mathrm{F}_{1}=\mu \mathrm{N}=0.4 \times 700=280 \mathrm{N}$
contact force $: \mathrm{F}=\sqrt{\mathrm{N}^{2}+\mathrm{f}^{2}}$
So $\mathrm{N} \leq \mathrm{F} \leq \sqrt{\mathrm{N}^{2}+\mathrm{f}_{1}^{2}}$
$700 \leq \mathrm{F} \leq \sqrt{700^{2}+280^{2}}$
$\Rightarrow 700 \mathrm{N} \leq \mathrm{F} \leq 754$
Standard 11
Physics
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