Rotational Motion Question

Question

A 4.00 m long, massless beam rests horizontally on a support of 3.00 m from the left end, as shown. A mass of m1 = 13.2 kg is attached by a string to the beam x1 = 2.325 m from the left end, while a second mass m2 is attached x2 = 0.756 m to the right of the support. If the beam is in static equilibrium, what is the value of mass m2?

Answer 1

Hey Bhak,

Without doing the math for you, I can say that this looks like a problem that will use the idea that the sum of the rotational moments about the support point will have to equal 0.

1. Each mass will cause a moment about the support equal to the weight (the force) times the distance from the support (the lever arm's radius, if you will)
2. One mass will cause a clockwise moment and the other will cause a counterclockwise moment
3. For the beam to be in static equilibrium, these moments must be equal in magnitude and opposite in their rotational direction.
4. Remember to find the mass m2 in kg, not just the weight of m2 in N.