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ICSE Class 10 Physics Question 12 of 20

Force — Question 14

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Question 14

When a boy weighing 20 kgf sits at one end of a 4m long see-saw, it gets depressed at its end. How can it be brought to the horizontal position by a man weighing 40 kgf.

Answer

As we know, the principle of moments states that

Anticlockwise moment = Clockwise moment

20Kgf×2m=40Kgf×d⇒d=20×240⇒d=1m20 Kgf \times 2m = 40 Kgf \times d \\[0.5em] \Rightarrow d = \dfrac{20 \times 2}{40} \\[0.5em] \Rightarrow d = 1m

So it is proved that horizontal position can be achieved if a person sits at a distance of 1m from the centre on the side opposite to the boy.