# Some physics help needed

#### Skyblitz

Hi, I'm having a bit of trouble with a problem..

basically the question is as follows:
A particle falling covers 64% of the entire height in its last second of the fall. What is the total height of the fall?

I've tried equating two formulas, and a few other things but I can't seem to go anywhere. Any help would be appreciated.

I also need clarification on something.. My teacher said that on a position-time graph, that if there is a portion that has constant velocity (ie, no curve but a straight line), that you can't have instantaneous velocity since you can't draw a tangent to a point.. but I was under the impression that instantaneous velocity was just the velocity and any given point of time?

Thanks!

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#### enigma

Staff Emeritus
Gold Member
Hi Skyblitz,

Post your equations which you tried, so we can see if/where there is a problem.

EDIT: Re the instantaneous velocity, you can have one. The subject which covers it is (dum, dum, dum, da!) calculus. Basically, you get the instantaneous velocity by taking two close points, and bringing them closer and closer together, watching what the intersecting line does. As the distance between the points approaches zero, the intersecting line becomes the tangent.

Last edited:

#### HallsofIvy

Homework Helper
As enigma said, show us what equations you have equated or other things you have done and we will guide you.

#### Skyblitz

Sorry I didn't post the equations as I fell asleep yesterday night after studying [zz)]

But I did, with some help, figure out how to do it.

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