A screw jack has a square single start thread with a pitch of $5$ mm and an effective

diameter of $35$ mm $.$ The operating handle is $0\mathrm{.}45$ m $.$ The coefficient of friction between the

screw and operating nut is $0\mathrm{.}25$ and the load carried is $250$ kg $.$ Calculate:

i$.$ the torque required to raise and lower the load

ii$.$ the efficiency of the jack as a lifting device

iii. its mechanical advantage when raising this load.

iv$.$ If the coefficient of friction is increased in this screw jack, how would this affect the

torque required to raise the load?