# Homework Help: Helicopter, travelling horizontally, is 82 m above the ground. The pil

1. Feb 10, 2013

### cmkc109

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

helicopter, travelling horizontally, is 82 m above the ground. The pilot prepares to
release a relief package intended to land on the ground 96 m horizontally ahead. Air
resistance is negligible. The pilot does not throw the package, but lets it drop. What is the
initial velocity of the package relative to the ground?

2. Relevant equations

3. The attempt at a solution

What I don't understand is the velocity. Since the package is just dropped, doesnt it mean it has no initial velocity?
The solution says it has a horizontal initial velocity but not a vertical initial velocity
Can someone explain the concept of this, thanks

2. Feb 10, 2013

### rcgldr

Re: helicopter, travelling horizontally, is 82 m above the ground. The

This part of the problem is worded poorly The pilot prepares to release a relief package intended to land on the ground 96 m horizontally ahead, since this could imply that there's preparation time before the package is dropped. I think you're just supposed to assume that the package lands 96 m horizontally ahead from it's release point (start of the drop) from the helicopter.

3. Feb 10, 2013

### cmkc109

Re: helicopter, travelling horizontally, is 82 m above the ground. The

i didnt even think about that details..i'm still on the basic steps understanding the velocities..i dont understand why vy = 0 when it is dropped downward

4. Feb 10, 2013

### rcgldr

Re: helicopter, travelling horizontally, is 82 m above the ground. The

The package is dropped from a helicopter that is travelling horizontally, so when dropped, the package initially has the same horizontal velocity as the helicopter.

5. Feb 10, 2013

### cmkc109

Re: helicopter, travelling horizontally, is 82 m above the ground. The

so initially v1x = helicopter velocity v1y = 0 since helicopter is travelling horizontally
then what about after it leaves the helicopter?
will there be a velocity in both x and y direction?

6. Feb 10, 2013

### rcgldr

Re: helicopter, travelling horizontally, is 82 m above the ground. The

Yes, do you know what the rule is about objects in free fall for velocity in x and y direction?

7. Feb 10, 2013

### cmkc109

Re: helicopter, travelling horizontally, is 82 m above the ground. The

not sure if i know the rules that u are referring to

8. Feb 10, 2013

### rcgldr

Re: helicopter, travelling horizontally, is 82 m above the ground. The

Has your class talked about objects in free fall or objects that are being accelerated by gravity? If so, your class should have included equations for an object in free fall.

In what direction is the package accelerating, and what is the rate of acceleration for an object in free fall (being accelerated by gravity)?

9. Feb 10, 2013

### cmkc109

Re: helicopter, travelling horizontally, is 82 m above the ground. The

honestly my teacher doesnt teach much..

for rate of acceleration ,a is always 9.8 m/s^2 (-g)
so can switch kinematics equations from a to -g .

10. Feb 10, 2013

### rcgldr

Re: helicopter, travelling horizontally, is 82 m above the ground. The

OK, so the rate of acceleration in the y direction is -9.8 m / s^2. The problem states that air resistance can be ignored, so there is no acceleration in the x direction. So can you now attempt to write the equations for acceleration, velocity, and position versus time, for both x and y directions? These should have been given to you in class or included in your class book, otherwise, it would take calculus or similar knowledge to derive these equations of motion for an object in free fall.

11. Feb 10, 2013

### cmkc109

Re: helicopter, travelling horizontally, is 82 m above the ground. The

are u talking about the five kinematics equations? i solved this question using those equations. I'm just not sure about the velocity . I know those things, but that doesnt mean i understand why..

12. Feb 10, 2013

### cmkc109

Re: helicopter, travelling horizontally, is 82 m above the ground. The

I am actually looking for explanation like this.

since this is a free fall question, the falling is only due to gravity but not vertical velocity. however, since the object is moving along with the plane at the instant it is being dropped, it has a horizontal velocity which is not due to free fall. once the object is dropped, only free fall is acting on the object .

can someone see if this is correct or elaborate on that please? thanks!

13. Feb 10, 2013

### rcgldr

Re: helicopter, travelling horizontally, is 82 m above the ground. The

14. Feb 10, 2013

### cmkc109

Re: helicopter, travelling horizontally, is 82 m above the ground. The

no , not answer, i am asking about the concept.. For physics , i believe it is better to understand the concept than just working out the answer. and my answer must be right because that is the sample question in the textbook...
does it mean my understanding of the question is wrong so u need to look at my work?

15. Feb 10, 2013

### rcgldr

Re: helicopter, travelling horizontally, is 82 m above the ground. The

Without seeing what those kinematic equations are, I can't tell if your method is correct.