Mathcad 15 - an error.
Prime 5 - a constant not function as an answer!
See the attach and help me please!
Two problems in your MC15 sheet:
1) wrong syntax of Odesolve (you don't have to provide the function name theta in MC15)
2) the expression on the right hand side of your ODE takes non-real values if theta goes above 45 degree
I coped boldly with the last situation by applying the Re() function 😉
Now you get a solution, but its constant 45°
Total energy is constant throughout, so the value under the square root sign of the numerator of the RHS of your ODE is always zero; hence theta goes nowhere (as you can see from Werner's graph)!!