The corvette crashes into the side of the disabled ISD, bringing it towards the second destroyer:
How can a small corvette shift big destroyers like this?
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Simple physics, really.
The destroyer is disabled, so it is unable to apply any force to change its own trajectory. In other words, when it lost power, it was locked into whatever course and speed it was moving (i.e. inertia).
The corvette, while far smaller, is clearly exerting a lot of lateral force on the star destroyer. It's also exerting it at the bow, where the rotational force would be greater. It's behaving just like a tug boat here, which is a small ship with a powerful motor to move larger ships that cannot maneuver easily.