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Car acceleration problem

  • #1
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Homework Statement


A car enters the freeway with a speed of 6.4 m/s and accelerates uniformly for 3.2 km in 3.5 minutes. How fast in m/s is the car moving after this time?

Homework Equations


DeltaX=1/2(vi+vf)(DeltaT)
Displacement=1/2(initial velocity + final velocity)(Time interval)

The Attempt at a Solution


3.2=1/2(6.4+x)(3.5)
x=-4.6
? Why is this negative? What is the final velocity?
 

Answers and Replies

  • #2
Nathanael
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It is important to be aware of which units you are using!
 
  • #3
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What do you mean? Do we need to convert the km to m first?
 
  • #4
Nathanael
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You need to convert everything into the same units, It only makes sense to add/subtract/cancel units which are the same.

For example, if I'm traveling 50 miles per hour, in 1 second will I have travelled 50*1=50 miles?
Of course not, because seconds are not the same as hours. (This is essentially what you did wrong.)
 

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