Problem solving process:

This problem is a typical travel problem.

According to the prompt: the propagation speed of lightning in the air is 0.33 km/s, and thunder is heard after 4 seconds.

According to the formula of travel problem: speed x time = distance.

0.33x4 =1.32km.

So the answer to this question is the distance of 1.32 km.

Extended data

The problem of travel is to study the movement of objects, which is a common problem in mathematics. Travel problem is an application problem that reflects the uniform motion of objects. Travel problems mainly include fairs, meetings, running water, train travel, clocks and watches.

Travel involves many changes, some involving the movement of one object, some involving the movement of two objects, and some involving the movement of three objects. There are three situations involving the movement of two objects: opposite movement (encounter problem), same movement (chase problem) and opposite movement (separation problem). But to sum up, whether it is the movement of one object or the movement of two objects, whether it is the opposite movement, the same movement or the opposite movement, their characteristics are the same. Specifically, they reflect the same quantitative relationship, which can be summarized as: S=vt (distance = speed × time).

Reference: Baidu Encyclopedia-Travel Problem Formula