# Homework Help: A plane going into (temporary) orbit

1. Jul 25, 2007

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

Early in the space program a jet aircraft was used to simulate "weightless" space flight. Beginning from a comfortable cruising altitude, assume such a craft could reach a speed of v = 590 m/s at an angle q = 30.9° above the horizontal. Subsequently the engines were used only to overcome air friction, and the plane followed a "free fall" path.

How long could "weightlessness" experiments be done before the plane fell back to its original altitude?

2. Relevant equations
I do not understand what the problem is asking me. I understand what free fall is and how it relates to orbit and "weighlessness" but I 'm not getting what they are asking.
I mean how does the angle play into orbit, if I dont know the original alititude??
Please someone help, --i just need question reasked in a different way ??
thanks for any help!

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jul 25, 2007

### mgb_phys

I agree - Ithink some of the question is missing

3. Jul 25, 2007

### PhanthomJay

I believe the problem is not asking about 'orbiting', but rather, it is referring to the parabolic path taken by the aircraft during it's 'free fall'. The problem isn't any different than asking how long a cannonball is in the air when it is fired at an initial speed at a certain angle. For the aircraft, since it is stated that the air friction is overcome just enough by the engines, then the only net force acting on the craft is the force of gravity, and hence, the plane and person is in 'free fall' just like the cannonball or a thrown ball or a person jumping from a tall building or an orbiting space ship. In all cases, the person or object's weight is still there, but since no normal force is acting, their weight is 'apparently' zero, (and you get that 'roller coaster' feeling in your stomach!). So to solve your problem, use the parabolic motion equations to solve for the time it takes to go from cruise altitude and back again to cruise altitude, using V_initial = 590m/s at 30.9 degrees.

Last edited: Jul 25, 2007
4. Jul 26, 2007

### mgb_phys

I assumed you would have to fly downward to get 'weightlessness' - I see the question is assuming you fly up in an arc and get weightless only for the second half of the trajectory.

5. Jul 26, 2007

### PhanthomJay

Actually, an object subject to gravity force and gravity force alone is in 'free fall' and 'apparently weightless' (zero G's) regardless of its direction of motion. So the astronaut is 'weightless' throughout the parabolic arc.

6. Jul 26, 2007

### mgb_phys

Of course it is, sorry - looks like my dream of becoming of 'vomit comet' pilot just went out the window!
(note to self: must not reply to physics questions just before going to bed)

Last edited: Jul 26, 2007