Question

Why is a jackscrew provided with a long arm?

Answer 1

Jack screw is used to lift heavy bodies like cars upward by rotating the handle (arm) which leads to the increasing height of the support pad. But humans can apply force up to a permissible extent which is too little to lift a car. So, huge torque is needed to move the support pad of jackscrew even by few centimeters up. And Torque produced by the body is directly proportional to both $r$ and F.
Where,
$r$ is the length from the axis of rotation
$F$ is applied force, which is perpendicular to the length.

Complete step by step answer:
We know Torque produced is given by $\overrightarrow \tau = \overrightarrow r \times \overrightarrow F$. In order to produce higher torque, we need either r or F or both to get increased by some factor depending on how much we want to increase. In case of Jack screw, which is used to lift heavy vehicles, this torque required is very high. Therefore, in order to reduce effort, we increase the arm of jackscrew longer. So that $\overrightarrow \tau = \overrightarrow r \times \overrightarrow F$ meets up the requirement up to permissible limits.
Additional Information: A jackscrew is device based on the principle of lever. It can be used to lift very heavy loads like loaded vehicles, cranes, trucks etc. just by using normal human efforts. A lever itself is a simple machine having three components. Load, Effort, and Support. Here, Jack load lifts heavy body (Load) and manpower provides effort, and jack threads are supports altogether forms simple machine. The arm of the jackscrew is attached to the effort end of this setup which enables torque to be passed into the system from a longer distance. All these together does the work. Hence, called a machine. There are various classes of the lever, most of which would be discussed in engineering in detail.

Note:
Higher torque makes the locked-thread of the jackscrew slide easily. This implies, higher the torque easier to rotate the body. One should also remember that arm length reflects the distance from the center of rotation or axis, which is given by r.