8th Grade Science
posted by Anya on .
A runner whose initial speed is 29 km/hr increases her speed to 31 km/hr in order to win a race. If the runner takes 0.5 seconds to complete this increase in speed, what is her acceleration?
I think it's either 1440 km/hr/hr
or 0.4 km/hr/sec. Are you supposed to convert the seconds? Thank you in advance.

This involves the acceleration formula.

a = change in velocity/change in time
change in velocity = 31000 m/hr/3600 s/hr  29000m/hr/3600 s/hr = .56 m/s
so
.56 m/s / .5 s = 1.11 m/s^2 
a= (31km/hr  29km/hr) / 5sec
a= 0.4 km/hr/s
That's how I got one of the answers....I am confused at what you are trying to show me. 
a= (Vf  Vi) / t