It's the first one . Thank you!skeeter said:
Mechanics is the branch of physics that deals with the study of motion and the forces that cause motion.
General motion in a straight line refers to the movement of an object along a straight path, where the velocity and acceleration of the object may change over time.
Speed is a measure of how fast an object is moving, while velocity is a measure of both the speed and direction of an object's motion.
Acceleration is the rate of change of an object's velocity over time. It can be calculated by dividing the change in velocity by the change in time.
Newton's first law of motion states that an object at rest will remain at rest, and an object in motion will continue moving in a straight line at a constant velocity, unless acted upon by an external force. This law is the basis for understanding the concept of inertia in mechanics.