An object will continue accelerating until
(a) the resultant force on it begins to decrease.
(b) the velocity changes direction.
(c) the resultant force on it is zero.
(d)the resultant force is at a right angle to its direction of motion.

Hint:In order to solve this question, we will use Newton’s laws of motion. Newton's Laws of Motion is a set of three laws that describe how the application of force disturbs the state of motion of an object.

Complete step by step answer:
According to Newton's second law, it describes the relationship between the force applied, and the acceleration produced in an object.
So, we know that,
\[Force(F) = mass(m) \times acceleration(a)\]
\[a = \dfrac{F}{m}\]
The mass of the object is constant and cannot be zero. So, we can say an object will continue accelerating until the resultant force on it is zero.

Thus, the correct answer to this question is option (c).

Additional Information:Newton's Laws of Motion is a set of three laws that describe how the application of force disturbs the state of motion of an object. The first law states that the state of motion of an object does not change unless a force is applied to it. The second law describes the relationship between the force applied, and the acceleration produced in an object. The third law describes how forces always come in pairs. Forces always occur in pairs. The force exerted by an object A on an object B is equal and opposite to the force exerted on A by B.

Note:While solving this question, we should be aware of Newton's second law, it describes the relationship between the force applied, and the acceleration produced in an object.