Modelling displacements and velocities

by The Open University

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1.3: Summing vectors given in geometric form

The following activity illustrates how the conversion processes outlined in the preceding sections may come in useful. If two vectors are given in geometric form, and their sum is sought in the same form, one approach is to convert each of the vectors into component form, add their corresponding components, and then convert the sum back to geometric form.

Activity 3 Finding the sum in geometric form, via components

Find the magnitude and direction of the sum of the two vectors which were specified in Activity 1 giving your answers correct to two decimal places. (You will need to choose different labels for the two vectors.)

Answer

Solution

Adopting the labels p and q for the two given vectors, you found in Activity 1(a) that the component forms were (to 4 d.p.)

Their sum is

The magnitude of the vector r = p + q is

Since the components of r are r 1 = 1.3231, r 2 = 1.9640, we have

Also, (1.3231, 1.9640) lies in the first quadrant, so the direction of r is θ =  φ ≈ 56.03°.

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