since the car starts at 60 km/hr, first subtract the 60 from 90 km/hr which is 30. that is the acceleration we need to solve. 2.0 m/s multiply by 60 seconds in a minute, and 60 minutes in an hour, which equals 7200 m/s in an hour or divide by 1000 (1000 meters in a km) and have 7.2m an hour. divide the 30 km/hr by 7.2 and you have 4.167 hours. You could also take the 30 km/hr needed to accelerate to match the 90 km/hr and find the number of meters needed to accelerate which is 30,000. divide by 2 meters per second equals 15,000. divide by 60 seconds in a minute, and divide by 60 minutes in an hour which still equals 4.167 hours.
