(4) A model rocket is launched, and the propellant burns until exhausted. After the propellant is exhausted, the rocket will continue to coast upward until gravity causes it to fall downward. Finally, a parachute will pop out and slow the descent of the rocket until it hits the ground. Below is a graph of the vertical VELOCITY of the rocket with respect to time in seconds after launch: 150 100 50 10 15 -50 -100 -150 Answer the following questions. (a) At what time did the rocket reach its highest point? What was its velocity then? (b) At what time did the parachute pop out? What was the velocity of the rocket at that time? (c) At what time did the engine stop? What was the velocity of the rocket at that time? (d) When did the rocket hit the ground? What was the velocity of the rocket just before hitting the ground?