Question

A 40 kg, 5.0-m-long beam is supported by, but not attached to, the two posts in Figure P12.60. A 20 kg boy starts walking along the beam. How close can he get to the right end of the beam without it falling over?

Short answer

He can walk up to 1 meter from the end without it falling over .

Step-by-step solution

Given information

Mass of beam = 40 kg,

length of beam = 5.0-m

supported by, but not attached to, the two posts as shown in figure

mass of boy = 20 kg

Explanation

First create the diagram as below

Then equate the clockwise and anti-clockwise torque.

Lets assume it can walk upto x m from right end , then solve for x.

$$\begin{gathered} W_b\times 0.5m=W\times (2m-xm) \\ 40kg\times g\times 0.5m=20kg\times g\times (2m-xm) \\ x=1m \end{gathered}$$