mgl = 1/2 m v^2l = v^2/(2g) = 4.8^2/如唤拦(2*9.8) = 1.17551 m频率链销 f = √渣胡(g/l)/(2π) = √(9.8/l.17551)/(2π) = 0.459536 s
方法,先用机械能守恒求解杆的长度L ,再带单摆公式求单摆震荡频率f