圆柱的体积=底面积乘以高=底的半径的平方乘以π乘高=45/2×0.01×45/2×0.01×π×2.5=0.39740625立方米，
V=SH=πr²H=3.14×(0.45÷2)²×2.5=3.14×0.05×2.5=0.39立方米
