# Motion along a Straight Line problem

An alert hiker sees a boulder fall from the top of a distant cliff and notes that it takes 1.30 s for the boulder to fall the last third of the way to the ground. You may ignore air resistance.

I have calculated the last 1/3 of the distance to be 8.281 m by the formula y=(1/2)(a)(t^2) where a=gravity=9.8 meters per second.
However to find the total distance of the cliff, I can't just multiply the distance of the last third times 3 because the boulder is accelerating throughout the entire distance, so how do I find the totatl distance?

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For some reaosn I'm stumped right now, but I can tell you that
I have calculated the last 1/3 of the distance to be 8.281 m by the formula y=(1/2)(a)(t^2) where a=gravity=9.8 meters per second.
doesnt work because
because the boulder is accelerating throughout the entire distance
applies to this part of the problem too.

Fermat
Homework Helper
You only have distance moved and time to work with. And gravity of course.

Let u be the velocity at beginning of last third
Let v be the velocity when stricking the ground.

Calculate u in terms of distance fallen
Calculate v in terms of distance fallen

The distance moved has been used. Can you now relate u and v in terms of t ?