A model rocket is launched straight upward. Its altitude
y as a function of time is given by y = bt - ct², where
b = 80 m/s, c = 4.9 m/s², t is the time in seconds, and y is in me-
ters. (a) Use differentiation to find a general expression for the rock-
et's velocity as a function of time. (b) When is the velocity zero?
謝謝～