Okay...who here knows Physics?

[tallahasseedem]

I have a couple of problems and I need help pronto! It has been years since I took it and dont remember a thing.


Duh! Here are the questions.

A bolt comes loose from the bottom of an elevator that is moving upward at a speed of 7.18 m/s. The bolt reaches the bottom of the elevator shaft in 2.85 s. How high up was the elevator when the bolt came loose?


What is the speed of the bolt when it hits the bottom of the elevator shaft?

[Redstone]

1. Well, what are your questions? We can't answer them if you

don't ask them.

Redstone

[tallahasseedem]

3. Sorry.

They are there now!

[Redstone]

4. They are WHERE now?

Redstone

[liontamer]

2. NNadir does

try PMing him

[mainegreen]

5. Acceleration

http://en.wikipedia.org/wiki/Acceleration

Acceleration of gravity ~9.8 m/s2

[petronius]

6. I'm going to say:

19.34 m up, and -20.75 m/s at impact. But I could be wrong, these answers are only worth as much as you paid for them...

[ChoralScholar]

8. I got the same number for terminal velocity.

I was sitting here trying to figure the distance up.

I haven't taken physics in years. I can, however, analyze an orchestral score by sight.

[petronius]

11. Cool, independent confirmation! I guess we have careers at NASA

waiting for us!

[tallahasseedem]

10. Alright big guy.

She just entered it into the Capa system and you were right! So how did you do it? Smarty pants!:P

[petronius]

12. It was pretty straightforward, really:

I built a remote-controlled quick-release clamp, attached it to the bottom of an elevator, broke into a high-rise office building, hacked the elevator computer so I could control the speed, obtained a super-accurate stopwatch and a laser-rangefinder, and conducted 30 independent experiments to get a best estimate of the unknown values...

[tallahasseedem]

14. Sweet.

I always love interactive physics problems.

[johnnie]

7. I don't believe in them

They are all just a scam.






















:)

[tallahasseedem]

9. LOL!

Thanks guys. I am trying to help a friend on a deadline and I havent done this crapola since way before grad school! We will see!

[Squeegee]

13. Here's the work

the formula for velocity would be (or the speed at which the bolt hits the ground):

v = v0 - gt

v = final velocity
v0 = initial velocity = 7.18m/s
g = acceleration of gravity = 9.8 m/s^2
t = time = 2.85 s

We want to solve for final velocity:

v = 7.18 - 9.8 * 2.85 = 7.18 - 27.93 = -20.75m/s (it's negative because it's in the oposite direction of its original direction of travel)



The formula for distance (in this case height from the floor where the bolt lands) would be something like:

y - y0 = v0t - 1/2gt^2

y = final height = 0 m
y0 = initial height
v0 = initial velocity = 7.18 m/s
g = acceleration of gravity = 9.8 m/s^2
t = time = 2.85 s

We want to solve for initial height:

0 - y0 = 7.18 * 2.85 - (1/2) * 9.8 * (2.85 ^ 2)
-y0 = 20.463 - 39.8 = -19.337
y0 = 19.337m

[tallahasseedem]

15. Thank you Squeegee.

I can always count on fellow DUers....I love this place!