# Homework Help: Kinetic projectile motion (Helicopter questions)

1. Sep 7, 2011

### bbalin23

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

A helicopter flies upward at 3.0m/s. The pilot drops a coke bottle when the helicopter is 30.0m above ground. How long will it take the coke bottle to hit the ground?
(2.8s)

*Note* We can't factor or use quadratics to solve

2. Relevant equations

3. The attempt at a solution

First I tried to calculate the distance the coke bottle will go upward before falling downward:

Vf2-Vi2/2a = d

9/19.62

0.459

Then I added that to the distance... D(total) = 0.459m + 30.0m = 30.459m

Then I attempted to find the time from there using the formula:

d = vi(t) + 1/2 a t(squared)

Vi from the maximum height (Total distance) is zero so

Sqrt(2d/a) = t

Sqrt(60.918/9.81)
Sqrt(6.20978)
t = 2.4919
= 2.5s

Last edited: Sep 7, 2011
2. Sep 7, 2011

### iRaid

Just use the equation normally. Don't calculate the first thing you did.

So basically just use:
$d=v_{i}t-4.9t^{2}+h$
h being the initial height.
Then you'll end up factoring and have 1 of the answers

3. Sep 7, 2011

### bbalin23

Sorry I forgot to mention it earlier but we weren't supposed to factor or use quadratic equations :(

4. Sep 7, 2011

### Spinnor

You only need one formula,

y = y_o + v_o*t + a*t^2/2

You know y_o, v_o, and a

5. Sep 7, 2011

### bbalin23

I'm not sure which formula that is unfortunetly as its not on my formula sheet, so I dont think I would be allowed to use it.

6. Sep 7, 2011

### iRaid

Why cant you factor lol?

7. Sep 7, 2011

### bbalin23

Apparantly we are supposed to be able to figure this out without factoring (She says its to refrain us from using calculus later on in the course as if we do we wont get marks on the question)

8. Sep 7, 2011

### bbalin23

Thanks everyone I figured it out using a couple different formulas! Thanks for helping!