In january 2004, nasa landed exploration vehicles on mars. part of the descent consisted of the following stages: stage a: friction with the atmosphere reduced the speed from 19300 km/h to 1600 km/h in 4.0 min. stage b: a parachute then opened to slow it down to 321 km/h in 94 s. stage c: retro rockets then fired to reduce its speed to zero over a distance of 75 m. assume that each stage followed immediately after the preceding one and that the acceleration during each stage was constant.