# Elevator and dropped book

#### caksez.14

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?

Gold Member
You need to show some formulas and some kind of attempt at a solution before you can receive assistance.

#### caksez.14

I can't solve the problem how can I attempt at a solution??

Gold Member
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

Gold Member
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?

#### caksez.14

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
We can't help you if you don't post your work!

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

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Gold Member
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.

Last edited by a moderator:

#### caksez.14

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

#### caksez.14

what is A what is B?

Gold Member
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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