Question

The classroom door is of width $50\text{cm}$. The force of $5\text{N}$ is applied on the handle which is situated in the middle of the smaller plate as shown below. Compute the torque about the hinge (lever arm) of the door.

• A. $3.5\text{Nm}$
• B. $1.5\text{Nm}$
• C. $2.5\text{Nm}$
• D. $2.0\text{Nm}$

Answer 1

The correct option is D $2.0\text{Nm}$


The handle of the door is located at $10\text{cm}$ as shown in the figure.
Thus, the line of action is $\frac{20}{2}=10\text{cm}$ from the outer edge.
Distance from axis of rotation or lever arm $=d=50-10=40\text{cm}=0.4\text{m}$
Force exerted $=5\text{N}$
Thus, torque $\left(\tau \right)=5\times 0.4$
$\tau =2.0\text{Nm}$