Free falling objects

  • Thread starter pberardi
  • Start date
  • #1
16
0

Homework Statement



The height of a helicopter above the ground is given by h = 3.00t^2, where h is in meters and t is in seconds. After 2.00s the helicopter releases a small mailbag. How long after its release does the mailbag reach the ground

Homework Equations


Xf = Xi + VxT + .5at^2


The Attempt at a Solution


h = 24
a = -9.8
Vi = 6.00t^2 at 2 = 24 m/s not sure about this

0 = 24 + 24t + .5(-9.8)t^2
t = 5.7

Did I go about this right? Please help.
 

Answers and Replies

  • #2
109
0

Homework Statement



The height of a helicopter above the ground is given by h = 3.00t^2, where h is in meters and t is in seconds. After 2.00s the helicopter releases a small mailbag. How long after its release does the mailbag reach the ground

Homework Equations


Xf = Xi + VxT + .5at^2


The Attempt at a Solution


h = 24
a = -9.8
Vi = 6.00t^2 at 2 = 24 m/s not sure about this

0 = 24 + 24t + .5(-9.8)t^2
t = 5.7

Did I go about this right? Please help.

Wouldn't the initial height be 12? 2^2*3 = 12?

Also, do you do physics with calculus? If so, you could take the derivative of the height function to get the velocity function, and simply plug in for t. If not, you can only get the average velocity, which won't do you any good in this problem, since the helicopter is accelerating.
 
  • #3
16
0
I am sorry, my mistake. I did do the calculus. But I wrote the height function incorrectly. It is supposed to be h = 3t^3

So based on this new information, is it correct?
 
  • #4
109
0
I am sorry, my mistake. I did do the calculus. But I wrote the height function incorrectly. It is supposed to be h = 3t^3

So based on this new information, is it correct?
The initial height is correct, but the derivative of 3t^3 is 9t^2. With that in mind, the initial velocity would be 36.
 
  • #5
16
0
Should be
0 = 24 + 36t + .5(-9.8)t^2
t = 7.96
?
 
  • #6
109
0
Should be
0 = 24 + 36t + .5(-9.8)t^2
t = 7.96
?
That looks good.
 
  • #7
16
0
Thank you sir.
 
  • #8
550
2
They might deduct a couple points if units aren't shown in every step ...
0 = 24.0 m + (36.0 m/s) t + (1/2) (-9.8 m/s^2) t^2
 
Last edited:

Related Threads on Free falling objects

  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
2
Views
3K
Replies
1
Views
2K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
3
Views
1K
Replies
3
Views
17K
Replies
7
Views
2K
  • Last Post
Replies
1
Views
952
  • Last Post
Replies
10
Views
2K
  • Last Post
Replies
6
Views
4K
Top