第一章-Mathematical Models in Mechanics(按照Edexcel课本顺序讲解,没有编辑完)

发布时间:2024年01月19日

Learning Objective
●理解数学模型如何应用到力学中
●理解假设 (Assumptions)如何在力学模型中利用
●知道7个标准单位以及在derived quantities中的使用。(下面前三个在M1必须掌握)

physical quantitysymbol
meterm
kilogramkg
seconds
ampereA
molemol
candelacd

是米(m),千克(kg),秒(s),安培(A),开尔文(K),摩尔(mol),坎德拉(cd)。

Prior Knowledge Check(预备知识)
1. 5 x 2 ? 21 x + 4 = 0 5x^2-21x+4=0 5x2?21x+4=0
2.在这里插入图片描述

3.30km/h to cm/s
4.0.003806

Example1
The motion of a basketball as it leaves a player’s hand and passes through the net can be modelled using the equation h = 2 + 1.1 x ? 0.1 x 2 h=2+1.1x-0.1x^2 h=2+1.1x?0.1x2, where h h h m is the height of the basketball above the groupd and x x x m is the horizontal distance travelled. "

a Find the height of the basketball:

i whenitis released ii at a horizontal distance of 0.5 m.
b Use the model to predict the height of the basketball when it is at a horizontal distance of 15 m

from the player.
c Comment on the validity of this prediction.

Solution
a首先绘制这个图

import numpy as np  
import matplotlib.pyplot as plt  
  
# 定义x的范围  
x = np.linspace(0, 15, 400)  
  
# 定义h函数  
h = 2 + 1.1*x - 0.1*x**2  
  
# 绘制h函数  
plt.figure(figsize=(8,6))  
plt.plot(x, h, label='h(x)')  
plt.title('h(x) = 2 + 1.1x - 0.1x^2')  
plt.xlabel('x')  
plt.ylabel('h(x)')  
plt.grid(True)  
plt.legend()  
plt.show()

在这里插入图片描述

根据图可以知道在y轴上的y=2的地方是篮球起抛点(考试时不要写中文,下同,注意这个只是讲义!

a i x = 0 ; h = 2 + 0 ? 0 Height = 2 m \begin{array}{|ll}\text{a}&\text{i}&x=0;h=2+0-0\\&&\text{Height}=2m\end{array} a?i?x=0;h=2+0?0Height=2m?

ii问的是在水平距离x=0.5的位置,球的高度是多少
ii x = 0.5 ; h = 2 + 1.1 × 0.5 ? 0.1 × ( 0.5 ) 2 Height = 2.525 m \begin{array}{rl}\text{ii}&x=0.5;h=2+1.1\times0.5-0.1\times(0.5)^2\\\text{Height}&=2.525m\end{array} iiHeight?x=0.5;h=2+1.1×0.5?0.1×(0.5)2=2.525m?

b Use the model to predict the height of the basketball when it is at a horizontal distance of 15 m from the player.
根据上面画的图可知,球都到地底下了了,所以模型不适用。
b x = 15 ; h = 2 + 1.1 × 15 ? 0.1 × ( 15 ) 2 Height = ? 4 m \begin{array}{ll} {x=15;h=2+1.1\times15-0.1\times(15)^{2}}\\{\text{Height}=-4m}\end{array} x=15;h=2+1.1×15?0.1×(15)2Height=?4m?

c?Comment?on?the?validity?of?this?prediction. \text{c Comment on the validity of this prediction.} c?Comment?on?the?validity?of?this?prediction.
c Height cannot be negative so the model is not valid when x=15m

文章来源:https://blog.csdn.net/appleyuchi/article/details/135699910
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