Helicopter Physics: Finding Time to Reach Ground from Release Point

[chocolatelover]

Homework Statement

The height of a helicopter above the ground is given by h=2.55t^3, where h is in meters and t is in seconds. At 1.85 s, the helicopter releases a small mailbag. How long after its release does the mailbag reach the ground?

Homework Equations

The Attempt at a Solution

_____________________________h=2.55t^3
1.85s

h=2.55(1.85s)^3

Thank you very much

 

[methotrexate]

I'm fairly sure that you can make use of the formula:

$$h=v_{i}t+\frac{1}{2}at^2$$

And do it as you started:

$$2.55(1.85)^3=v_{i}t+\frac{1}{2}at^2$$

And then initial velocity is zero, and a is the gravitational constant $$g=9.8m/s^2$$:

$$2.55(1.85)^3=0t+\frac{1}{2}9.8t^2$$

And then solve for t.

 

[physixguru]

I'm fairly sure that you can make use of the formula:

$$h=v_{i}t+\frac{1}{2}at^2$$

And do it as you started:

$$2.55(1.85)^3=v_{i}t+\frac{1}{2}at^2$$

And then initial velocity is zero, and a is the gravitational constant $$g=9.8m/s^2$$:

$$2.55(1.85)^3=0t+\frac{1}{2}9.8t^2$$

And then solve for t.

WHO IN THE WORLD TOLD YOU THAT THE INITIAL SPEED OF THE BAG IS ZERO?

 

[chocolatelover]

Thank you very much

If it isn't 0, how would you solve it?

Would you do this?

velocity:
h=3.25t^3
h'=9.75t^2
h'(1.65)=9.75(1.62)^2
=26.5444

position:

h=3.25(1.65)^3
=14.6m

I would then use all of this to solve for t, right?

h=vit+1/2at^2
14.6m=26.5444m/s+1/2(-9.8m/s^2)t^2
t=1.56s

Thank you