Quandaries and Queries


Name: Debbie

Question: I am taking college physics I and need some help! I do not even know where to begin!!


The general equation for a parabola is y = ax 2 + bx + c, where a, b, c are constants. What are the units of each constant if y and x are in meters?

Please help me!!



Hi Debbie,

The point here is that you can only add quantities that have the same units. We multiply quantities of different units (eg. to get foot-pounds) and divde quantities of different units (eg. to get miles/hour) but for addition we need the quantities to be of the same units. Hence if x is in meters and y is in meters then we must have

  • c in meters
  • bx in meters, and
  • ax 2 in meters.

Since x is in meters and bx is in meters, b must have no units, we might say b is unitless.

Since x is in meters, x 2 is in meters 2. Thus since ax 2 is in meters, a must have the units of one-over-meters.

I hope this helps,

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