一、利用动量定理求物体的动量变化 例1将质量为5 kg的物体以v0=6 m／s的速度 从足够高处抛出,经t=4 s其速度变为vt．求该物体在 这4 s内的动量变化(不计空气阻力,g取10 m／s2)． 分析与解:由于物体的初、末速度方向均未知,故 无法用△p=p2-p1来求解,而动量定理为我们提供了 求动量变化的另一种方法． 物体在空中运动过程中仅受重力(恒力),故合力 的冲量就是重力的冲量．由动量定理有: △p=IG=mgt=5×10×4 kg·m／s=200 kg·m／s, 方向竖直向下 First, the use of the momentum theorem to find the momentum of the object changes Example 1 mass of 5 kg object v0 = 6 m / s speed from high enough to throw out, after t = 4 s its speed becomes vt. Find the momentum change of this object within 4 s (excluding air resistance, g takes 10 m/s2). Analysis and solution: Since the initial and final velocity directions of the object are unknown, it cannot be solved with △p=p2-p1, but the momentum theorem provides us with another method to find the change of momentum. Objects are only subjected to gravity (constant force) during the air movement, so the impulse of the resultant force is the impulse of gravity. The momentum theorem is: △p=IG=mgt=5×10×4 kg·m/s=200 kg·m/s, direction is vertical downward