Runga-Kutta help needed (Matlab)

[Mech-Master]

An object of mass m falls from rest at a point near the Earth's surface. If the air resistance is proportional to the velocity v^2, the differential equation for the velocity as a function of time is given by:

m*dv/dt = mg - cv^2

a) Derive the exact solution

done this part, and i got v = sqrt(m*g/c)*tanh(t*sqrt(g*c/m))

b) For the given paraments g = 9.81 m/s^2. m = 68.1 kg and c = 1.5 kg/m. plot the exact solution and the numerical solution v(t) obtained from the 4th order predictor-corrector runge kutta methods using an interval of dt = 0.25 seconds in the domain of 0<t<6

i'm having trouble coding the runge kutta method with all the k1, k2, k3 and k4.. I really need help with this.

Thanks

 

[matematikawan]

Matlab already has a built-in Runge-Kutta solver, probabaly ode45. So I think you need not have to worry about those k_i's.