# An acceleration problem

Discussion in 'MCAT Study Question Q&A' started by z32019912, Sep 23, 2014.

1. ### z32019912 2+ Year Member

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Jun 17, 2013
Hello,

So the question states that theres a barrel that's 1m in length and the time spent in barrel was not given.
the cannon ball starts from rest and exit with speed of 50m/s. The question asks for Acceleration.

The answer key gave an alternate short cut saying the object go from 0 to 50m/s, and it had an average velocity of 25m/s in barrel. And you can find the time it requires to travel the barrel with that avg velocity which can be used to divide by time to find acceleration.

what I don't get is, how is the average velocity 25m/s if there was no time elapsed in the barrel given?

3. ### BobRSanchez

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Sep 23, 2014
Average velocity can be figured out by asking simply this: What is the average between 0 and 50? Answer: 25.

The velocity begins at 0, and ends at 50. Time is not necessary to find the average velocity if you are given a starting velocity and an ending velocity.

4. ### z32019912 2+ Year Member

29
3
Jun 17, 2013
isnt the average velocity found from elapsed time? so at this case we would be assuming that 2 seconds were spent from 0 to 50?

5. ### BobRSanchez

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Sep 23, 2014
Average velocity is given by either [v(final) + v(initial)] / 2. OR by displacement/time it took for displacement to occur.

With your way, dividing velocity by time (seconds) would give you acceleration, not velocity. Units can be an important indicator of whether you are performing calculations correctly.

29
3
Jun 17, 2013
thank you