EasyPhysicsHigh School (11–12)Mechanics › Relative MotionMechanics › Motion in a Straight LineConceptualNumerical
Train A goes at 90 km/h and train B at 63 km/h, the same way on parallel tracks.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Train A goes at and train B at , the same way on parallel tracks. Find the velocity of A relative to B, in km/h and in m/s.
Need a reminder? The key ideaShow
Along a line, , with signs. The same way: subtract the speeds. Opposite ways: add them. Time to meet gap closing speed. To change km/h to m/s, multiply by .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. , forward.
Step 2. .
Answer: , in the direction of motion.
Check. A passenger in B sees A creep ahead slowly; from the ground A is far faster. Both views are right.
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