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8th Grade Science

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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 - ,

    This involves the acceleration formula.

  • 8th Grade Science - ,

    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 - ,

    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 - ,

    a= (Vf - Vi) / t

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