One dimensional stress,strain,deflection analysis

[tanma_amnat]

hi
i am an undergrad student

i had an eqn like the following from which i am to find deflection,stress and strain using finite difference method

EI (d⁴ y/dx⁴)-m(d²y/dt²)-P sin wt=0

P=force
y=deflection
w=frequency
t=time

i have developed a MATLAB prog for deflection

how can I find stress and strain now?

i am confused which formula should i use?
should i find moment first and then stress or is there any other way?

just tell me the way, not the prog

 

[tanma_amnat]

its urgent...
i will be very greatful if someone gives an advice