Theory question 106
StaticsA uniform beam, WX, of length 90 cm and weight 50 N is suspended on a pivot, 35 cm from W. It is kept in equilibrium by means of forces T and 20 N applied at Y and Z respectively. |WY| = 10 cm and |XZ| = 10 cm. Find the value of T.
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Model answer
Positions from W: Y at 10 cm, pivot at 35 cm, centre of the beam at 45 cm, Z at 80 cm.
Taking both forces downwards, moments about the pivot: T × 25 = 50 × 10 + 20 × 45 = 500 + 900.
T = 1400/25 = 56 N.
Explanation
Don't forget the beam's own weight acting at its midpoint.