an automobile traveling in a straight line at the speed of 70 km/hrs, slow down to 50 km/hrs in 5 seconds. What is the average acceleration?
70 km/h * 1000 m/km * 1 h/3600 s
= 19.44 m/s
so
50 km/h = 13.89 m/s
a = change in v/change in t
= (13.89 - 19.44)/5
= - 1.11 m/s^2