14. The coordinates of an object moving through R3 are

for time t > 0, where a, b, and c are constants. What is the speed of the object at time t?

A.

B.

C.

D.

E.

 

Solution: The answer is E

 

Let P(t) be the position vector that describes the moving object and is defined as,

So that the speed of the object at time t is the magnitude of the tangent vector P’(t), which is given by,