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Corollary

COROLLARY

Suppose X = F(t) is a curve whose distance |F(t)| from the origin is a constant r0. Then the derivative F'(t) is perpendicular to F(t) whenever F'(t) ≠ 0.

PROOF

We use the Inner Product Rule. For all t,

10_vectors-245.gif

Therefore

F(t) · F'(t) = 0, so F(t) ⊥ F'(t),

as shown in Figure 10.7.6.

10_vectors-246.gif

Figure 10.7.6

We see from the corollary that if a particle moves with constant speed |V| = v0, then its acceleration vector is always perpendicular to the velocity vector (Figure 10.7.7).

10_vectors-247.gif

Figure 10.7.7 Motion with Constant Speed


Last Update: 2006-11-06