答案是：k1*k2/k1+k2设有质量为m的物体挂在L1上伸长为x1,在L2上伸长为x2在连起来的弹簧上伸长为X3有mg=k1x1=k2x2=k3x3有因为连起来后两弹簧互相拉力相等,均为mg,所以X3=X1+X2所以k3=mg/（x1+x2）=mg/{mg/(k1+mg/k2)}...