A 44kg , 5.2-m-long beam is supported, but not attached to, the two posts in the

Question

A 44kg , 5.2-m-long beam is supported, but not attached to, the two posts in the figure (Figure 1) . A 25kg boy starts walking along the beam.

How close can he get to the right end of the beam without it falling over?

Express your answer to two significant figures and include the appropriate units.

A 44kg , 5.2-m-long beam is supported, but not attached to, the two posts in the figure (Figure 1) . A 25kg boy starts walking along the beam. How close can he get to the right end of the beam without it falling over? Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

At the farthest, let us use the right beam as the axis of rotation.

Let x = the distance from the right

Hence,

2.2 -x = moment arm with respect to the right beam

The COM of the bar acts on its middle, which is0.4 m from the right beam.

At farthest to the right, the left beam exerts no normal force.

Thus, summing torques,

44 kg (9.8 m/s^2) (0.04) - 25 kg (9.8 m/s^2)(2.2 - x) = 0

Solving for x,

x = 2.13 m   [ANSWER, distance from the right end]

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