Elevator and dropped book

  • Thread starter caksez.14
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While riding on an elevator descending with a constant speed of 3.2 , you accidentally drop a book from under your arm.How long does it take for the book to reach the elevator floor, 1.0 below your arm?
 

JJBladester

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You need to show some formulas and some kind of attempt at a solution before you can receive assistance.
 
I can't solve the problem how can I attempt at a solution??
 

JJBladester

Gold Member
286
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What is going on in the problem?
- Constant acceleration (due to gravity)... Here are your constant acceleration equations:

vf2=vi2+2a(x2-x1)

vf=viat

Okay... So let's see what the problem gives you.

Firstly, you know that gravity accelerates things down at 9.81m/s2... That's what "a" is.

You know the initial velocity and the change in height (x2-x1) from the problem. Can you find vf?

Once you know vf, let's see if you can find t with the equations given...
 

DaveC426913

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I can't solve the problem how can I attempt at a solution??
Why do you think that? Did you not attend the class? Do you not have your textbook?
 
time is 0.45 I found that then Of course I can found final velocity however my result is wrong. What is the book's speed relative to you when it hits the elevator floor? asks question
 

DaveC426913

Gold Member
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1,512
We can't help you if you don't post your work!


Also, you erased the template provided. Why did you do that?

Rules:
On posting questions: Any and all high school and undergraduate homework assignments or textbook style exercises for which you are seeking assistance are to be posted in the appropriate forum in our Homework & Coursework Questions area

NOTE: You MUST show that you have attempted to answer your question in order to receive help. You MUST make use of the homework template, which automatically appears when a new topic is created in the homework help forums. Once your question or problem has been responded to, do not go back and delete (or edit) your original post..
 

JJBladester

Gold Member
286
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Show your work. How did you find time? How did you find velocity?

This is the formula for relative velocity. It says that the velocity of A equals the velocity of B plus the velocity of A with respect to B.

[URL]http://upload.wikimedia.org/math/2/f/5/2f5a92923c17aea5a83160b242065b10.png[/URL]
 
Last edited by a moderator:
I'm finding velocity from 'vf2=vi2+2a(x2-x1)' as 5.5 m/s however this result is wrong...

our Vi should be 3.2
a=9.8
and x=1
 
what is A what is B?
 

JJBladester

Gold Member
286
2
Elevator
vi = -3.2 m/s
a = 0m/s2
yi(floor)=0m
Using the constant acceleration equation yf = yi + vi(t)=(1/2)a(t)2
Set up an equation for yf(floor)

Book

vi = -3.2 m/s
a = -9.81 m/s2
yi(book) = 1m

Using the constant acceleration equation yf=yi+vi(t)+(1/2)a(t)2
Set up an equation for yf(book)

________________________________________________
You know that the book and the floor are in the same final position at the end of the drop,right? I mean, the book rests on the floor so they must have the same yf. Knowing this, how could you solve for t after setting the equations above up with actual values?
 

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