📚 Work-Energy Theorem and Its Applications | 动能定理及其应用
The work-energy theorem is one of the most powerful and frequently examined concepts in A-Level Physics. It links Newton's laws of motion to the concept of energy, providing a direct, scalar alternative to solving mechanics problems. This article explores the theorem in depth, its derivation, and its extensive applications across various physical scenarios.
动能定理是A-Level物理中最重要且最常考查的概念之一。它将牛顿运动定律与能量概念联系起来，为求解力学问题提供了一种直接的标量方法。本文将深入探讨该定理的推导过程及其在各种物理情境中的广泛应用。
1. Understanding Work Done | 理解做功
tude of the force, s is the magnitude of the displacement, and θ is the angle between the force vector and the displacement vector.
做功是指力使物体发生位移时所做的功。数学上，做功W定义为力与沿力方向位移的乘积：W = F × s × cosθ，其中F为力的大小，s为位移的大小，θ为力矢量与位移矢量之间的夹角。
Work is a scalar quantity measured in joules (J), where 1 J = 1 N⋅ the force is perpendicular to the displacement (θ = 90°), cos90° = 0 and no work is done.
功是标量，单位为焦耳（J），1 J = 1 N⋅m。cosθ因子意味着只有平行于位移方向的分力才对做功有贡献。如果力与位移垂直（θ = 90°），则cos90° = 0，此时不做功。
It is essential to distinguish between positive and negative work. When the force component is in the same direction as the displacement, the work is positive; when it opposes the displacement, the work is negative. Friction, for example, always does negative work on a moving object.
区分正功与负功至关重要。当力的分力与位移同向时，做功为正；当分力与位移反向时，做功为负。例如，摩擦力对运动物体所做的功始终为负。
2. Kinetic Energy | 动能
Kinetic energy is the energy an object possesses due to its motion. For an object of mass m moving with speed v, its kinetic energy Eₖ is given by the equation:
动能是物体由于运动而具有的能量。对于质量为m、以速度v运动的物体，其动能Eₖ由下式给出：
Eₖ = ½mv²
Kinetic energy is a scalar quantity and is always positive or zero, never negative. It depends on both the mass of the object and the
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