A block of mass $M$ placed on rough surface of coefficient of friction equal to $3$ . If $F$ is the $(4/5)$ of the minimum force required to just move. Find out the force exerted by ground on the block
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The force exerted by ground on the block

=$\sqrt {{N^2} + {f^2}} $

=$\sqrt {{{\left( {Mg} \right)}^2} + {{\left[ {\left( {\frac{4}{5}} \right)\left( {3Mg} \right)} \right]}^2}} $ = $\frac{{13}}{5}Mg$ = $2.6Mg$

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