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6. system of particles and rotational motion — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysics6. system of particles and rotational motion1 Mark
MCQ
A uniform cube of side $a$ and mass $m $ rests on a rough horizontal table. $A$ horizontal force $F $ is applied normal to one of the faces at a point that is directly above the centre of the face, at a height $\frac{{3a}}{4}$ above the base. The minimum value of $F$ for which the cube begins to tilt about the edge is (assume that the cube does not slide)
  • A
    $\frac{{mg}}{4}$
  • ✓
    $\frac{{2mg}}{3}$
  • C
    $\frac{{3mg}}{4}$
  • D
    $mg$
✓

Answer

Correct option: B.
$\frac{{2mg}}{3}$
b
The minimum force for which cube begins to tilt, the normal reaction should pass through the tilting edge point $'O’.$

Taking moments about point $O,$

$F \times \frac{3 a}{4}=m g \times \frac{a}{2}$

$\Rightarrow F=\frac{2}{3} m g$

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