Thread: Past papers with brief solutions :(

Ive been going through exam papers and theres a question on differential equations which I cant get to grips with

m*dv/dt = mg-kv [g> k/mv]

dv/dt= g-kv/m

∫dt = ∫g-kv/m dv

im not sure on how to integrate this can anyone help explain it?

This is a linear ODE, and you want to write it in standard form:



Now, calculate the integrating factor and multiply the ODE by this:



Now, the left side is the differentiation of a product:



Can you proceed from here?

Do you know how to use an Integrating factor - Wikipedia, the free encyclopedia?

The integration for dt is simply "t".
The expression on the RHS is being integrated with respect to "v" so you should treat everything else as a constant and then proceed.
The expression ∫g-kv/m dv = g∫dv- k/m∫vdv
= gv- k/m(v^2/2)+c

Hope this helps.

hey thanks that helps alot guys I should be able to go from here thank you