# Fundamental of Physics 10th Edition Problem 52

1. Aug 31, 2014

### kmshowalter

1. The problem statement, all variables and given/known data

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?

2. Relevant equations

3. 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)

2. Aug 31, 2014

### SteamKing

Staff Emeritus
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.

3. Aug 31, 2014

### kmshowalter

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

4. Aug 31, 2014

### SteamKing

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

http://mathematicsi.com/deriving-suvat-equations-motion/ [Broken]

Last edited by a moderator: May 6, 2017