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Question
Solve the following problem.
A 2 m long wooden plank of mass 20 kg is pivoted (supported from below) at 0.5 m from either end. A person of mass 40 kg starts walking from one of these pivots to the farther end. How far can the person walk before the plank topples?
Solution
Let the person starts walking from pivot P2 as shown in the figure.
Assume the person can walk up to distance x from P1 before the plank topples. The plank will topple when the moment exerted by the person about P1 is not balanced by a moment of force due to plank about P2.
∴ For equilibrium,
40 × x = 20 × 0.5
∴ x = `1/4` = 0.25 m
Hence, the total distance walked by the person is 1.25 m.
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