Question

A square plate of side 4 metre has uniform mass density and is hinged at the midpoint of one of its edge as shown in the figure. What will be the torque due to gravity on it about the hinged point A? (Mass of the plate = $20kg$; g = $10m{s}^2$)

• A. 200 N-m
• B. 100 N-m
• C. 400 N-m
• D. 300 N-m

Answer 1

The correct option is C

400 N-m

The force of gravity can be assumed to act on its centre of mass.
${\left|\right(\overrightarrow{{\tau }_A}\left)\right|}_{clockwise}=\frac{MgL}{2}$

$=\frac{20\times 10\times 4}{2}Nm$
= 400 Nm