## Statement

difficulty

If a body is in the position (1,2) and after 2 seconds it is in the position (1,-2).

What will be its average velocity considering that all units are expressed in the International System?

## Solution

Since we are using International System units, the two positions respectively called Pi and Pf are expressed in meters.

Initial data

Pi (1,2) m y Pf(1,-2) m.
Δt=t2-t1=2 sg.

Resolution

To calculate the average velocity, we must use of the following equation:

where the time elapsed is already provided in the statement and the displacement vector is obtained of the following way:

$∆\stackrel{\to }{r}={\stackrel{\to }{r}}_{f}-{\stackrel{\to }{r}}_{i}=\left({x}_{f}-{x}_{i}\right)\stackrel{\to }{i}+\left({y}_{f}-{y}_{i}\right)\stackrel{\to }{j}+\left({z}_{f}-{z}_{i}\right)\stackrel{\to }{k}$

Therefore, first we calculate the displacement vector regarding these two positions:

Once we know the displacement vector, we can calculate the average velocity vector.

## Formulas worksheet

These are the main formulas that you must know to solve this exercise. If you are not clear about their meaning, we recommend you to check the theory in the corresponding sections. Furthermore, you will find in them, under the Formulas tab, the codes that will allow you to integrate these equations in external programs like Word or Mathematica.

Formulas
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