Question

The mass of a metallic beam of uniform thickness and of length $6m$ is $60kg$. The beam lies horizontally and symmetrically on two vertical pillars which are separated by a distance $3m$. A person of mass $75kg$ is walking on this beam. The closest distance to which the person can approach one end of the beam so that the beam does not tilt down is (neglect thickness of pillars):

• A. $30cm$
• B. $20cm$
• C. $15cm$
• D. $10cm$

Answer 1

The correct option is A $30cm$

For tilting down, $N_2$ should just equal to zero.
Therefore calculating torque about A,
Torque = Force X displacement.
$75g\times d=60g\times 1.5$

$d=\frac{60\times 1.5}{75}$

$=1.2m$
Distance from the left end
$=1.5m-1.2m=0.3m$
$=30cm$