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# Physics/motion in one dimension

Question
QUESTION: A car starting from rest acquires a velocity 180 m s ^-1 in 0.05 h . Find the acceleration.

Acceleration = change in velocity / elapsed time
That formula gives average acceleration. If the acceleration is constant during the time period, the formula gives the car's acceleration at any moment during the 0.05 h period. (We don't have any information about that, so I guess we should call our result the average acceleration.)

So the car's
average acceleration = (180 m/s - 0) / 0.05 h = 3600 m/s.h

Those units are valid, but unconventional. Generally we want acceleration with units of m/s^2. So perhaps conversion to the normal units would be good. Note that an hour contains 3600 seconds.

3600 m/s.h * 1 h/3600 s = 1 m/s^2

I hope this helps,
Steve

---------- FOLLOW-UP ----------

QUESTION: A car travels 100 m with a constant accerleration  and average velocity of 20 ms^-1.the final velocity acquired  by the car is 25 ms^-1.find : (1)the initial velocity of the bus (2)the distance travelled by bus during this time.

Hello again astina,

1. You can find the time required to travel those 100 m using the average velocity.
Vave = d/t
Solve for t and plug in 25 ms^-1 and 100 m for Vave and d.

Then use the kinematic formula
d = ((Vi + Vf)/2)*t
Plug in 25 ms^-1 for Vf and solve for Vi.

2. The distance traveled was given -- 100 m.

I hope this helps,
Steve
Questioner's Rating
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Physics

Volunteer

#### Steve Johnson

##### Expertise

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.

##### Experience

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.

Education/Credentials
BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University