Posted by **Anya** on Tuesday, January 10, 2012 at 8:51pm.

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.

- 8th Grade Science -
**Anya**, Tuesday, January 10, 2012 at 8:52pm
This involves the acceleration formula.

- 8th Grade Science -
**Damon**, Tuesday, January 10, 2012 at 9:01pm
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

- 8th Grade Science -
**Anya**, Tuesday, January 10, 2012 at 9:07pm
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.

- 8th Grade Science -
**Anya**, Tuesday, January 10, 2012 at 9:12pm
a= (Vf - Vi) / t

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