It is easier to turn the steering wheel of a large diameter than that of a small diameter. Give reason.

A spanner (or wrench) has a long handle. Why?

The adjacent diagram shows a heavy roller, with its axle at O, which is to be raised on a pavement XY. If there is friction between the roller and pavement, show by an arrow on the diagram the point of application and the direction of force to be applied. If pivoted at 0, now will it go up?

Define the moment of a couple. Write its S.I unit.