Two children push on opposite ends of a uniform 3 m board pivoted at its centre. One pushes 4 N at the 0 cm end; the other pushes 6 N at the 300 cm end, both perpendicular to the board. The board:
ASlides without rotating
BRotates anticlockwise
CStays in equilibrium
DRotates clockwise
Answer & Solution
Correct answer: D. Rotates clockwise
1. Pivot is at the 150 cm mark.
2. The 4 N push at the 0 cm end has lever arm 150 cm and acts anticlockwise (say).
3. Anticlockwise moment = 4 × 150 = 600 N·cm.
4. The 6 N push at the 300 cm end has lever arm 150 cm and acts clockwise.
5. Clockwise moment = 6 × 150 = 900 N·cm.
6. Clockwise moment is larger by 300 N·cm.
7. Net torque is clockwise, so the board rotates clockwise.
8. Options B and C ignore the magnitude difference; option D confuses translation with rotation.
_Source: Selina Concise Physics ICSE Class 10, Ch 1 'Force' (icsehelp.com chapter extract)_
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