"""
Ex. 5.9 from "A Primer on...
The exercise requires that you read arguments for v0
from the command line, so the program must be run
from the terminal. If you run it using the button in VS 
code or spider, the variable v0_list will be an empty
list, none of the code lines inside the for loop will be run, 
and the resulting plot will be empty. 
"""


import numpy as np
import matplotlib.pyplot as plt
import sys

#v0 = 10
v0_list = sys.argv[1:]

g = 9.81

for v0 in v0_list:
    v0 = float(v0)
    t = np.linspace(0, 2*v0/g, 101)
    y = v0 * t - 0.5 * g * t**2
    plt.plot(t,y)
    
plt.xlabel("time (s)")
plt.ylabel("height (m)")
plt.show()

"""
Terminal> plot_ball2.py 10 12 20
(output is a plot)
"""