Kinetic projectile motion (Helicopter questions)

[bbalin23]

Homework Statement

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

Homework Equations

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

Im off by .3 please help!

 

[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

 

[bbalin23]

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

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

 

[Spinnor]

You only need one formula,

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

You know y_o, v_o, and a

 

[bbalin23]

You only need one formula,

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

You know y_o, v_o, and a

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

 

[iRaid]

Why can't you factor lol?

 

[bbalin23]

Why can't you factor lol?

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 won't get marks on the question)

 

[bbalin23]

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