運動方程式 - II

The second kinematic equation expresses an object's final position as the sum of its initial position, the distance moved under constant initial velocity, and the distance traveled due to acceleration. This equation applies only when acceleration remains constant throughout the motion, allowing you to calculate position at any time t.

The derivation uses two expressions for average velocity over a time interval. The first defines average velocity as change in displacement over change in time. The second represents average velocity as the mean of initial and final velocities. Substituting the first kinematic equation into this relationship yields the position equation.

Position consists of three components: the initial position x0, the distance traveled at constant initial velocity, and the distance covered during the velocity change caused by acceleration. Together, these components determine where an object is located at any given time t during constant acceleration motion.

Rearranging the second kinematic equation produces a quadratic equation in time. Using the quadratic formula yields two mathematical solutions. However, only the positive solution is physically meaningful, since negative time would indicate an event occurring before motion began, making it unreasonable to accept.

Yes. For a car merging onto a 200 m ramp with initial velocity 10 m/s and acceleration 2 m/s², substitute these known values into the second kinematic equation. Solving the resulting quadratic equation gives t = 10 s as the valid solution, meaning the car takes 10 seconds to travel the ramp.

The second kinematic equation is derived assuming constant acceleration, which allows average velocity to be expressed as the mean of initial and final velocities. If acceleration varies, this relationship breaks down, and the equation no longer accurately predicts position, making constant acceleration a fundamental requirement.

The second kinematic equation builds on the first kinematic equation, which relates velocity to acceleration. Together with concepts like average velocity and instantaneous velocity, these equations form a complete framework for analyzing motion with constant acceleration and solving kinematic equations problem solving scenarios.