you walk up the aisle in a bus moving 10m/sec and a seated friend you are walking 1.5m/sec. another friend who just got off the bus standing there waving at you says you are moving 11.5m/sec.and the stalker friend riding his bike next to the bus say your speed is 0m/sec. which friend is right.
both if they are measuring speed RELATIVE to them.
Julia rides her bike 10 km north with a constant speed of 12 kph and another 15 km north with a constant speed of 12 kph.
How long does the trip take?
What is her average speed?
What is her average velocity?
To determine which friend is right, let's break down the relative motion of each person in relation to each other and the ground.
1. You are walking up the aisle in the bus, which is moving at 10m/sec. Your speed relative to the ground is the sum of your walking speed and the bus's speed. Therefore, your speed is 10m/sec + 1.5m/sec = 11.5m/sec.
2. Your seated friend is not moving relative to the bus, so their speed relative to the ground is simply the speed of the bus, which is 10m/sec.
3. The friend who just got off the bus and is waving at you is not moving in relation to the ground. Since they are stationary, their speed is 0m/sec.
4. The stalker friend who is riding their bike next to the bus sees you moving up the aisle but does not take into account the bus's motion. From their perspective, you are not moving relative to the ground, so they say your speed is 0m/sec.
Based on these explanations, the friend who is correct about your speed relative to the ground is the friend who just got off the bus and claims your speed is 0m/sec.