(2)弹性力的功 A2 F=ko F=-(-0 入 12=Fdr k(r-lo) d(r. r) (2)=a 2 2 12 2-KO=)=2[ k 2=( 2 2（2）弹性力的功 F = k 0 0 F = −k(r −l )r   = − −  =  2 1 0 0 12 ( ) A A A A k r l d W d 2 1 r r F r d r dr r d r d r dr =  =  = ( ) = 2 1 ( ) 2 1 2 0 r r r r r [( ) ( ) ] 2 ( ) 2 2 0 2 1 2 0 1 0 2 1 r l r l k W k r l dr r r = − − = − − −  ( ) 2 2 2 2 12=  1 − k W