每日一题 | A-Level物理-弹簧串并联劲度系数，同学们快来做题打卡吧！

【A-Level物理-弹簧串并联劲度系数】

A number of similar springs，each having the same spring constant，are joined in three arrangements X，Y and Z.The same load is applied to each.

What is the order of increasing extension for these arrgements?

 

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 昨日 [ 每日一题 ] 答案 

Integration by parts： 

Use Integration by parts to find ∫xsin3x dx ；

Using your answer to part 1,find ∫x^2cos3x dx。

1.u=x dv=sin3x du=1 v=-1/3cos3x

=∫xsin3x-1/3xcos3x+1/9sin3x+Cdx=-3xcos3x- ∫-1/3cos3x dx

2.u=x^2 dv=cos3x du=2x v=1/3sin3x

∫x^2cos3xdx=1/3x^2sin3x-2/3 ∫xsin3xdx =1/3x^2sin3x-2/3{-1/3cos3x+1/9sin3x}+C =1/3x^2sin3x+2/9xcos3x-2/27sin3x+C