A ball is thrown upward in the air by a passenger on

a train that is moving with constant velocity.

a. Describe the path of the ball as seen by the

passenger. Describe the path as seen by a stationary

observer outside the train.

b. How would these observations change if the

train were accelerating along the track?

So I now understand that to the passenger in the train moving at constant velocity, the ball would appear to go up and down in a straight line. And I sort of see that to the observer outside, the ball would appear to go forward in the air in a downward arc.

But for part b, it seems the answer is that the ball would appear to move in a parabolic arc to both people. But I was wondering, is there any difference in the arcs that they both see (like in the length of the arc or something else.

Also, if the train is accelerating and the ball is thrown straight up, does that mean that the ball lands behind the person who threw it and would thus be a backwards arc?

Ask yourself this question: Would the path of the ball as seen by the ground observer change due to what happens to the train after the ball leaves the hand of the passenger?

Yes. You have got it.

Perhaps a another way to phrase Janus' hint is

 

What causes the ball to accelerate?

Oh I see, so it doesn't matter what the train is doing since the ball leaves the hand at the same velocity and gravity is constant anyway.

 

But for my other question, does the ball land behind the person when the train is accelerating?

Oh I see, so it doesn't matter what the train is doing since the ball leaves the hand at the same velocity and gravity is constant anyway.

 

But for my other question, does the ball land behind the person when the train is accelerating?

 

What are your thoughts? Imagine you're in a constantly accelerating train. What would it feel like?

You have entitled this thread relative velocity.

 

Acceleration is also a vector so you could consider relative acceleration, and again answer my question,

 

What causes the (relative) acceleration?

Is this question dealing with frame of references? It seems like they can be 2 point of view, the ground observer and the passanger on the train. You mean accelerating downwards becuase of gravity or accelerating forwards for a brief moment due to addition of velocity by the accelerating train before dropping towards the floor?