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course Phy 121
re-submit
An automobile traveling a straight line is at point A at clock time t = 4 sec, where it is traveling at 10 m/s, to point B at clock time t = 11 sec, where it is traveling at 20.5 m/s. Point A is 75 meters from the starting point and point B is 115 meters from the starting point. What are the average velocity and the average acceleration of the automobile during the specified time? What evidence is there that the acceleration is or is not uniform?
Average velocity between the start and point A is 5 m/s. You can't know this, since you don't know its velocity at t = 0, nor do you know whether the acceleration is constant.
Average velocity between point A and point B is 15.25 m/s.
If acceleration was constant this would be accurate. However you can't assume constant acceleration. You can find the average velocity using the definition of average velocity, and should do so.
If acceleration is uniform, then average velocity is the average of initial and final velocities. If acceleration isn't uniform, it's unlikely that this is the case.
Average velocity between the start and point B is 10.25 m/s.
you don't know when or where this situation started, or fast the car was going at the start
The acceleration between the start and point A is (10 m/s)/(4 seconds) or 2.5 m/s^2.
The acceleration between point A and point B is (10.5 m/s)/(7 seconds) or 1.5 m/s^2.
This is the average acceleration, since acceleration can't be assumed constant.
The acceleration between the start and point B is (20.5 m/s)/(11 seconds) or 1.9 m/s^2.
The acceleration is not uniform as evident by the results of the three rates of acceleration.
See my notes and please do submit a revision. Shouldn't take you long, but there are important lessons here and it will be worth your time.
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