Question

why jackscrew is provided with the longarm

Answer 1

The jack screw provided with a long arm because in order to produce maximum turning effect of the screw jack the force is applied at point of body for which the distance from the axis should maximum so that the given force provides maximum torque to turn the screw jack. 
since torques = force * perpendicular distance .......
here torque is directly proportional to the distance that's why for maximum turning effect jack screw provided with a long arm........
mark as brainliest

Answer 2

here jack screw is used to rotata the jack . this rotation i given by the movement