3.3.K.sagews

from sympy import *
from sympy import N as Num

# SI units:
m  = Symbol("m",  positive=True)
s  = Symbol("s",  positive=True)
kg = Symbol("kg", positive=True)

print("\n--- User input -----------------------")

symbolic = True

if symbolic:
    # quantity = symbol:
    g = var("g")
    r, R = var("r, R")
    m1,m2 = var("m1,m2")
    Theta = var("Theta")
    mu = var("mu")

print("\n--- d: -------------------------------")

a2, S1, S2, N = var("a2, S1, S2, N")

eq1 = Eq(Theta*a2/R, R*S2 - r*S1)
eq2 = Eq(m1*r/R*a2, S1 - mu*N)
eq3 = Eq(0, m1*g - N)
eq4 = Eq(m2*a2, m2*g - S2)

eqs = [eq1, eq2, eq3, eq4]
sol = solve(eqs, [a2, S1, S2, N])

a2 = sol[a2]
pprint(["a2: ", a2])

print("\n--- e: -------------------------------")

a2=a2.subs(m1,m)
a2=a2.subs(m2,m)
a2=a2.subs(Theta,m*R*R/2)
a2=a2.subs(r,R/2)
a2=a2.subs(mu,S(1)/2)

pprint(["a2: ", a2])

--- User input ----------------------- --- d: ------------------------------- R*g*(R*m2 - m1*mu*r) [a2: , ---------------------] 2 2 R *m2 + Theta + m1*r --- e: ------------------------------- 3*g [a2: , ---] 7