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Ch 03: Motion in Two or Three Dimensions
Chapter 3, Problem 3

The position of a squirrel running in a park is given by r = [(0.280 m/s)t + (0.0360 m/s2)t2]î + (0.0190 m/s3)t3ĵ. (b) At t = 5.00 s, how far is the squirrel from its initial position?

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Identify the position function of the squirrel. The position vector is given by \( r = [(0.280 \, \text{m/s})t + (0.0360 \, \text{m/s}^2)t^2] \hat{i} + (0.0190 \, \text{m/s}^3)t^3 \hat{j} \).
Substitute the given time \( t = 5.00 \, \text{s} \) into the position function to find the position of the squirrel at that time. Calculate \( r(5.00) \) by plugging in \( t = 5.00 \, \text{s} \) into each component of the vector.
Calculate the initial position of the squirrel at \( t = 0 \, \text{s} \) by substituting \( t = 0 \) into the position function, resulting in \( r(0) \).
Determine the displacement vector \( \Delta r \) by subtracting the initial position vector \( r(0) \) from the position vector at \( t = 5.00 \, \text{s} \), i.e., \( \Delta r = r(5.00) - r(0) \).
Calculate the magnitude of the displacement vector \( \Delta r \) to find how far the squirrel is from its initial position. Use the formula for the magnitude of a vector: \( |\Delta r| = \sqrt{(\Delta x)^2 + (\Delta y)^2} \), where \( \Delta x \) and \( \Delta y \) are the components of the displacement vector.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Position Vector

A position vector describes the location of an object in space relative to a reference point, typically the origin of a coordinate system. In this case, the position of the squirrel is given as a function of time, incorporating both linear and nonlinear components. The vector notation indicates movement in two dimensions, represented by the unit vectors î and ĵ.
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Kinematics

Kinematics is the branch of mechanics that deals with the motion of objects without considering the forces that cause the motion. It involves analyzing position, velocity, and acceleration as functions of time. In this problem, the position function of the squirrel allows us to determine its displacement over a specified time interval.
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Displacement

Displacement is a vector quantity that represents the change in position of an object. It is calculated as the final position minus the initial position. In this scenario, to find how far the squirrel is from its initial position at t = 5.00 s, we evaluate the position vector at that time and compare it to the position at t = 0.
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Related Practice
Textbook Question
A remote-controlled car is moving in a vacant parking lot. The velocity of the car as a function of time is given by v = [5.00 m/s − (0.0180 m/s3)t2]î + [2.00 m/s + (0.550 m/s2)t]ĵ. (b) What are the magnitude and direction of the car's velocity at t = 8.00 s? (b) What are the magnitude and direction of the car's acceleration at t = 8.00 s?
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Textbook Question
A 124-kg balloon carrying a 22-kg basket is descending with a constant downward velocity of 20.0 m/s. A 1.0-kg stone is thrown from the basket with an initial velocity of 15.0 m/s perpendicular to the path of the descending balloon, as measured relative to a person at rest in the basket. That person sees the stone hit the ground 5.00 s after it was thrown. Assume that the balloon continues its downward descent with the same constant speed of 20.0 m/s. (a) How high is the balloon when the rock is thrown?
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Textbook Question
A 124-kg balloon carrying a 22-kg basket is descending with a constant downward velocity of 20.0 m/s. A 1.0-kg stone is thrown from the basket with an initial velocity of 15.0 m/s perpendicular to the path of the descending balloon, as measured relative to a person at rest in the basket. That person sees the stone hit the ground 5.00 s after it was thrown. Assume that the balloon continues its downward descent with the same constant speed of 20.0 m/s. (c) At the instant the rock hits the ground, how far is it from the basket?
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Textbook Question
The coordinates of a bird flying in the xy-plane are given by x(t) = αt and y(t) = 3.0 m − βt2, where α = 2.4 m/s and β = 1.2 m/s2. (a) Sketch the path of the bird between t = 0 and t = 2.0 s.
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Textbook Question
The nose of an ultralight plane is pointed due south, and its airspeed indicator shows 35 m/s. The plane is in a 10–m/s wind blowing toward the southwest relative to the earth. (a) In a vector-addition diagram, show the relationship of υ→ P/E (the velocity of the plane relative to the earth) to the two given vectors.
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