Question

Two boxes are on opposite ends of a plank that is 3.0 m long. The plank is supported in the middle by a fulcrum. The box on the left has a mass, m1, of 25 kg. The box on the right has a mass, m2, of 15 kg. Use the formulas below to determine how far the fulcrum must be positioned from the right side of the plank in order to balance the masses horizontally. (Hint: g=9.8m/s2

Answer 1

For a given condition above, use the concept of equal moments. Moment is the product of the force and its distance from a reference point. Let x be the distance of the 25 kg body from the fulcrum and 3 - x be the distance of the right mass, 15 kg, from the fulcrum. Equating the moments give,
                            (25 kg)(9.8 m/s²)(x) = (15 kg)(9.8 m/s²)(3 - x)
The value of x is 1.125 m. Therefore, the fulcrum should be 1.875 m from the right mass.