Chapter 11: Q. 21 (page 901)
Principal unit normal vectors: Find the principal unit normal vector for the given function at the specified value of t.
, where and are positive,
Short Answer
Ans: The principal unit normal vector of at is
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Chapter 11: Q. 21 (page 901)
Principal unit normal vectors: Find the principal unit normal vector for the given function at the specified value of t.
, where and are positive,
Ans: The principal unit normal vector of at is
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Evaluate and simplify the indicated quantities in Exercises 35鈥41.
Annie is conscious of tidal currents when she is sea kayaking. This activity can be tricky in an area south-southwest of Cattle Point on San Juan Island in Washington State. Annie is planning a trip through that area and finds that the velocity of the current changes with time and can be expressed by the vector function
where t is measured in hours after midnight, speeds are given in knots and point due north.
(a) What is the velocity of the current at 8:00 a.m.?
(b) What is the velocity of the current at 11:00 a.m.?
(c) Annie needs to paddle through here heading southeast, 135 degrees from north. She wants the current to push her. What is the best time for her to pass this point? (Hint: Find the dot product of the given vector function with a vector in the direction of Annie鈥檚 travel, and determine when the result is maximized.)

Given a twice-differentiable vector-valued function , why does the principal unit normal vector point into the curve?
Given a vector-valued function r(t) with domain what is the relationship between the graph of r(t) and the graph of kr(t), where k > 1 is a scalar?
For each of the vector-valued functions in Exercises 22鈥28, find the unit tangent vector.
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