# Solving for a Vector

Question:

Show that if vector r x (d(vector r)/(dt)) = 0, |vector r| is constant.

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#### Solution Preview

Let us assume r_vector = r*(i_cap * cos(theta) + j_cap * sin(theta))

here unit vector along the direction of r_vector: r_cap = (i_cap * cos(theta) + j_cap * sin(theta))

as magnitude of r_vector = r = constant (given)

Therefore,

dr_vector/d(theta) = r * d(r_cap)/d(theta) = r * (i_cap*(-sin(theta)) + j_cap * ...

#### Solution Summary

This solution is comprised of a detailed, step by step response which explains how to solve this vector based problem.

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