How long will it take for a truck to come to a full stop after going 25 m per s at an acceleration rate of -7.7 ms2 How long will an object take to fall 154 feet from an initial velocity of 0 m per s?
the first question is rather simple to answer:
the truck is going at 25 meters per second and decelerating at 7.7 meter per second every second1 therefore after 1 second it will loose 7.7 MPS (meters per second) of speed. after 2 seconds it will loose 15.4 MPS. after 3.24 seconds, it will loose 25 MPS, coming to a full stop.
1("meters per second" is a speed measure, acceleration and deceleration is a change in speed and therefore we need to know the rate of change, i.e. how much speed (meters per second) it losses or gains every second. that is why we are using the term "meters per second every second")