Fundamental of Physics 10th Edition Problem 52

[kmshowalter]

Homework Statement

A bolt is dropped from a bridge under construction, falling 83 m to the valley below the bridge. (a) How much time does it take to pass through the last 20 % of its fall? What is its speed (b) when it begins that last 20 % of its fall and (c) just before it reaches the ground?

Homework Equations

The Attempt at a Solution

For part (a) I got the correct answer of .436 seconds by doing 83/4.9=16.94, sqrt16.94=4.12
83 x .20 = 16.6
83-16.6=66.4
66.4/4.9=13.55
sqrt13.55=3.68
4.12-3.68=.436

That answer was correct but I need parts (b) and (c)

 

[SteamKing]

Knowing the time something is falling under gravity, how do you calculate the velocity? You've learned one equation of kinematics; there's a couple more equations you need to learn as well.

 

[kmshowalter]

I'm sorry but that really doesn't help my understanding of how to do it.

 

[SteamKing]

It means there are some other equations that you need to learn:

http://mathematicsi.com/deriving-suvat-equations-motion/