So, I'm riding in a train and throw a ball...

I’m on a train going 100 mph and toss a ball to my friend inside the train. The ball travels at 25 mph. So from a stationary point outside the train the ball going 125 (or 100). What if I toss the ball out the window to someone standing by the tracks. Does the ball hit the person at 100 mph?

Confused and feeling ignorant.


Disregarding drag etc, yes - a ball dropped from the window of a moving train continues to move at the velocity of the train until it hits something.

The ball’s velocity can be modeled as a three-dimensional vector; each dimension has a separate magnitude. So let’s assume the train is traveling in a perfectly straight line east, and you throw the ball exactly north. Relative to the ground, it will travel north at 25mph, while also traveling east at 100mph, yielding a diagonal line (as compared to the tracks, for instance.)

And note that drag is simply the name we give to the effects that result from the ball hitting something - in this case, air molecules.

If you throw the ball perpendicular to the train’s direction, it will be going a trifle over 103 mph:

Velocity = sqrt( 100[sup]2[/sup] + 25[sup]2[/sup] ) = 103.08