Select the SI unit of moment of couple from the given below options.

A wheel of radius, $R$ with an axle of radius, $\frac{R}{2}$ is as shown in the figure and is free to rotate about a frictionless axis through its center and perpendicular to the page. Three forces $\left(F, F, 2 F\right)$, are exerted tangentially to the respective rims as shown in the figure.

The magnitude of the net torque acting on the system is nearly, 

Why does a spanner have a long handle?

Alongside diagram shows $\mathrm{AB}=25 \mathrm{cm}, \mathrm{BC}=75 \mathrm{cm}$. Calculate the distance the efforts moved, if the load is raised by $5 \mathrm{cm}$.

Alongside diagram shows $\mathrm{AB}=25 \mathrm{cm}, \mathrm{BC}=75 \mathrm{cm}$. Calculate the minimum effort required to raise the load of $20 \mathrm{kgf}$.

A uniform metre ruler balances horizontally on a knife edge placed at the $58 \mathrm{cm}$ mark when a weight of $20 \mathrm{gf}$ is suspended from one end. Draw a diagram of arrangement.

In the given diagram wheel shown has a fixed axle passing through $O$. The wheel is kept stationary under the action of two force $F_1$ and $F_2$ such that (i) a horizontal force $F_1$ at $P$ (ii) a vertical force $F_2$ at $Q$. Show the direction of $F_2$ in the diagram. Which is the greater force? Find the ratio between the forces.
(Given : $PO=2.5 \mathrm{cm}$, $QO\text{'}=1.5 \mathrm{cm}$ and $OO\text{'}=2.0 \mathrm{cm}$)