A jack screw is provided with a long arm. Explain 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?

What do you mean by equilibrium of a body?

State the condition when a body is in

(i) static equilibrium.

(ii) dynamic equilibrium.

Give one example each of static and dynamic equilibrium.