Final answer:
Newton's First Law of Motion, or the law of inertia, states that a force is necessary to cause an object to change its state of motion, including bringing it out of rest or altering its velocity if it's in motion.
Step-by-step explanation:
According to Newton's First Law of Motion, option c: 'a force is necessary to cause an object to leave its state of rest' is correct. This law, also known as the law of inertia, indicates that an object will not change its state of motion unless a net external force acts upon it. This means:
- A body at rest will remain at rest unless acted upon by a net external force.
- A body in motion will maintain its constant velocity and direction (straight line) unless acted upon by a net external force.
Therefore, it is inaccurate to say that a force is needed to maintain constant velocity (option a), that an object at rest will always stay at rest without qualifying 'unless acted upon by a net external force' (option b), or that once an object is in motion a force cannot change its velocity (option d).