Question

Change in speed would continue as long as an unbalanced force is applied ?

Answer 1

When multiple unbalanced forces are applied to a single object, then the object moves in the direction of the resultant force.

Complete answer:
The change in speed can be easily predicted by understanding the acceleration of that body.
When an unbalanced force is applied to a body, the acceleration of that body can be calculated using the formula $a=\dfrac{F}{m}$, where $F$ is the force and $m$ is the mass of that body. As the force is not zero, the body must be accelerating.Hence, an unbalanced force is required to accelerate the motion of a body and this motion is along with the resultant force.

Therefore, first, we have to determine the net unbalanced force and the acceleration of the body will be in that direction if the body starts from rest and the acceleration will be in some other direction if the body is already in motion, depending on various factors like magnitude and direction of the initial movement.In either way, the body accelerates. And if the body accelerates, the change in speed is inevitable.

Hence if an unbalanced force is applied, the change in speed will continue as long as the force exists.

Note: If you want to know the direction of the body’s movement, then remember to use the resultant or the net unbalanced force instead of following the illogical logic that says the movement will be in direction of the greater force.