If you're riding on a train going 50mph and you throw a ball forward...?

Question

at 50mph, how fast is the ball moving?

Answer 1

Relative to the ground, the ball is moving at 100 mph. You can just add the velocities.

You can prove this by analyzing it carefully, Say you're in the back of the car, and you throw the ball forward just as you (the back of the train) happen to pass a certain telephone pole. Say the ball travels for 1 second. You can calculate where the back of the train will be after 1 second (based on the train's speed). You can also calculate the position within the car where that ball ends up (based on the ball's speed relative to the train). So add up those two distances, and that's how far the ball has traveled, past the telephone pole. Divide that total distance by 1 second, and that's the ball's speed relative to the ground.

It turns out (if you do this calculation) that the ball's speed relative to the ground, is just the train's speed (50 mph) plus the ball's speed inside the train (50 mph).

If you threw the ball toward the BACK of the train, then you would find that you need to SUBTRACT the two velocities.

And if you threw the ball PERPENDICULAR to the train's motion (for example, train is going north, and you throw the ball west), then it gets a little more complicated. You can still calculate it, but you have to use a mathematical tool called vectors. In this case, the ball's speed (relative to ground) would be something like 71 mph.

Answer 2

there are two valid answers...the ball is going 50mph relative to you and the train and 100mph relative to a stationary observer outside the train. this is a rudimentary example of relativity.

Answer 3

100 MPH to an observer who is not on the train and on the ground.
50 MPh to the observers on the train.
150 MPH to the observer on the train going 50 MPH in the opposite direction.

Does this help?

Answer 4

depends which way you throw the ball.

if you throw the ball in the opposite direction of the train, then the balls travels at 0mi/hr ralative to the ground but at 50mi/hr ralative to the train

if you throw the ball in the same direction of the train, then the ball travels 100 mi/hr ralative to the ground and 50mi/hr ralative to the train

Answer 5

if your frame of reference is from the inside of the car, it is traveling at 50 mph.

If from outside it is 100mph if thrown in the same direction as the vehicle is travelling. If thrown the opposite direction 0 mph.

Very Einsteinian thought experiment...

Answer 6

Relative to you at rest in the train or relative to the train's motion.

Answer 7

50 mph backwards, 'cause it's probably bounced off someone's head & I've been kicked off the train!!!