import turtle


turtle.shape('turtle')
Vx, Vy = 5, 50
t = 0
dt = 0.2
ay = -3
x, y = 0, 0
turtle.up()
dx0, dy0 = 250, 100
turtle.goto(-dx0, -dy0)
turtle.down()
while True:
    t += dt
    x += Vx * dt
    y += Vy * dt + ay * dt**2/2
    Vy += ay * dt
    turtle.goto(x - dx0, y - dy0)
    if y <= 0:
        Vy = -Vy * 0.8