Assume you drop a bag of snacks inside an airplane that is flying due west at 800 km/h. Which of the following is true?, (check the description)

Question

I had this question in a quiz (MCQ). The choices were:

A) the bag moves southwest at speed greater than 800km per

 

B) the bag will fall straight down (south)

 

 

Actually there are two more choices but they are completely wrong.

 

My teacher told me that answer B is the correct,  but i disagree because motion can not be described without a reference point 

and in the question there are no reference point therefore I assumed two scenarios :

 

A is the correct if the reference point is a point on the earth's surface 

 

B is the correct if the reference point is the person who dropped the bag 

 

 

In the quiz I'm not allowed to choose two answers so i choose A and lost a point 

 

 

 

Is the question badly made or am I wrong in any way ??  

Answer 1

When released, the bag has an initial horizontal velocity that is the same as the velocity of the plane, so it will fall vertically down at constant acceleration, with a constant horizontal velocity of 800 km/h west.  In the reference frame of the moving plane, it will appear to be strictly a vertical drop.  In the reference frame of a point fixed on the surface of the earth, the trajectory will be a parabola. 

 

I agree the answer choices are poorly worded.  As literally worded, all the choices are wrong.

Answer 2

The bag will fall straight down -- not Southward, but toward the source of gravity (roughly the center of the Earth; note "drop"), since the plane is "flying."  The direction of flight -- here it is "due west" -- and the speed of flight (since the bag is inside the plane and is travelling at the same speed as the plane) are not relevant.

 

You are correct that the question is poorly worded.  Why?  Both South and Southwest are perpendicular to the source of gravity and "straight down (south)" is not an accurate description.  It is not the southward direction for flying at a constant altitude. It is "down" but not "south."