EasyPhysicsHigh School (11–12)Mechanics › Relative MotionMechanics › Motion in a Straight LineNumerical
A car moves at 28 m/s and a truck at 19 m/s on a straight highway.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A car moves at and a truck at on a straight highway.
- If they move in the same direction, what is the velocity of the car relative to the truck?
- If they move towards each other on opposite lanes, how fast does the gap between them close?
- In case (a), the car is long and the truck . How long does the overtaking take?
Need a reminder? The key ideaShow
Along a line, the velocity of A relative to B is
Same direction: the difference of the speeds. Opposite directions: their sum.
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. Same direction. , forwards.
Step 2. Opposite. .
Step 3. Overtaking. .
Answer: (a) . (b) . (c) .
Check. In the car goes and the truck : the car gains .
Watch out. Using only the truck's length gives ; the car's own length counts too.
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