Answer: - 30 miles / h^2
Explanation:
This problem requieres that you assume uniformly accelarated motion.
1) Data:
Vo = 60 miles / h
Vf = 30 miles / h
t = 12 min
a = ?
2) Formula:
Vf = Vo + at
3) Clear t:
a = [Vf - Vo] / t
4) convert t = 12 min to hours
t = 12 min * 1 h / 60 min = 0.2 h
5) Substitute the data into the formula
a = [30 miles/h - 60 miles/h]/0.2 h = - 30 miles / h^2
The negative sign means that the car decelerated.
Answer: - 30 miles / h^2
