You are on a train traveling east at speed of 12 m/s with respect to the ground.

Question

You are on a train traveling east at speed of 12 m/s with respect to the ground.

1)If you walk east toward the front of the train, with a speed of 2.6 m/s with respect to the train, what is your velocity with respect to the ground?

2)If you walk west toward the back of the train, with a speed of 3.9 m/s with respect to the train, what is your velocity with respect to the ground?

3)Your friend is sitting on another train traveling west at 18 m/s. As you walk toward the back of your train at 3.9 m/s, what is your velocity with respect to your friend?

Answer 1

Here is the answer to part one.

The speed of the train east is +12m/sec.

Your speed (east) is + 2.6 m/sec.

Your speed is (+12m/sec) + (+2.6 m/sec) = 14.6 m/sec.

When you move west, your speed becomes negative.

For example, if your speed is 2.6m/sec west, we denote it like

-2.6 m/sec. We can find the ground speed for the example:

(+ 12 m/sec) + (-2.6 m/sec) = 9.4 m/sec.

Part 3: If your friend is moving west 18 m/sec, the ground is moving 18 m/sec east according your friend. You need to add that speed to your speed, found in part 2.

I hope you can answer parts 2 and 3. Just follow the principle above. If your final speed is negative, this means the speed is in west direction.