Having trouble on this question:

The random variable Y with a density function given by

f(y)=[[(m)y^(m-1)]/(a)]*e^[(-y^(m))/(a)] where y is between 0 and infinity and a,m are greater than zero

is said to have a Weibull distribution. Find the mean and variance for a Weibull distributed random variable with m=2.

I can find the answers on the Internet somewhere, but how do you actually derive them?

Thanks for any help.

Jack