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A vehicle travels 80km at 100km/h, and 50 km at 75 km/h. What is the average speed of the vehicle?

I looked at the formula for average acceleration
( av. A = v2 - v1 / t2 - t1) ...However, the questions asks for the average "speed" of the vehicle.

Hello Tavis,

The average speed is calculated from the total distance traveled divided by the total time spent.

So you need to determine the time that elapsed in the 2 parts of the trip. Use the basic speed formula,
speed = distance/time,
and use your algebra skills to convert it to a form that gives you time on the left side of the equal sign with distance and speed on the right side.

Then calculate the elapsed time in the 2 parts of the trip. Add the 2 distances and the 2 times and plug them into the average speed formula on the first line above.

I hope this helps,


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Steve Johnson


I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.


I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University

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