Vector Equations and Particle Motion

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Questions and Answers

What is the expression for the velocity vector ~v of the particle at time t?

  • tî - 3t^2 ĵ + 4t^3 k̂
  • 2tî - 3t^2 ĵ + 4t^3 k̂ (correct)
  • 2tî - 3ĵ + 4k̂
  • 2tî - 3t ĵ + 4k̂

What is the acceleration vector ~a of the particle at t = 1?

  • 2î - 6ĵ + 12k̂ (correct)
  • 2î - 3ĵ + 4k̂
  • 2î - 3t^2 ĵ + 4t^3 k̂
  • 2î - 6t ĵ + 12t^2 k̂

What is the formula for velocity as derived from the position vector ~r(t)?

  • d~r/dt = î + 3ĵ + 4k̂
  • d~r/dt = t^2 î - t^3 ĵ + t^4 k̂
  • d~r/dt = 2tî - 3t^2 ĵ + 4t^3 k̂ (correct)
  • d~r/dt = î - ĵ + k̂

At time t = 1, what components make up the velocity vector ~v?

<p>2, -3, 4 (A)</p> Signup and view all the answers

What is the expression for the gradient of φ if φ = xyz?

<p>yz î + xz ĵ + xy k̂ (D)</p> Signup and view all the answers

At the point (1,-1,2), what is the value of grad φ when φ = xyz?

<p>-2î + 2ĵ - k̂ (A)</p> Signup and view all the answers

How do you calculate the magnitude of the gradient |∇φ| at the point (2,-1,1) for φ = x² + y² + z² + 2xyz?

<p>√(2^2 + 2^2 + (-2)^2) (B)</p> Signup and view all the answers

What is the gradient expression for φ = x² + y² + z² + 2xyz?

<p>(2x + 2yz)î + (2y + 2xz)ĵ + (2z + 2xy)k̂ (B)</p> Signup and view all the answers

What remains constant in the expression of the gradient ∇φ when φ = 2x³y²z⁴?

<p>The powers of x, y, and z. (D)</p> Signup and view all the answers

What will be the divergence of the vector field F~ = ∇φ at the point (1,-1,1) for φ = 2x³y²z⁴?

<p>24 (B)</p> Signup and view all the answers

What is the expression for the divergence of the vector field F~?

<p>12xy z + 4x z + 24x y z (A)</p> Signup and view all the answers

What is the curl of the vector field F~ = ∇φ at the point (1,-1,1) for φ = 2x³y²z⁴?

<p>(0, 0, 0) (B)</p> Signup and view all the answers

What does the curl of the vector field F~ equal at any point?

<p>0 (D)</p> Signup and view all the answers

Which of the following is true about the gradient vector field?

<p>It points in the direction of the maximum rate of increase of the scalar field. (C)</p> Signup and view all the answers

At the point (1,-1,1), what is the calculated divergence of F~?

<p>40 (C)</p> Signup and view all the answers

Which term is not part of the expression for the curl of F~?

<p>8x3 yz4 (D)</p> Signup and view all the answers

How is the divergence of vector field F~ computed?

<p>By summing the first partial derivatives of the components. (B)</p> Signup and view all the answers

What is the coefficient of the î component in the vector F~?

<p>6x2 y2 z4 (B)</p> Signup and view all the answers

Which of the following is part of the vector F~ equation?

<p>2x3 yz4 (B)</p> Signup and view all the answers

What is the form of the operator used to calculate divergence?

<p>∇· (A)</p> Signup and view all the answers

What is the computed value of div F~ at point (1,-1,1) if each component yields 12xy z, 4xz, and 24xy z respectively?

<p>40 (D)</p> Signup and view all the answers

What is the expression for the force field F~ given in the problem?

<p>(2x - y + z)î + (x + y - z 2 )ĵ + (3x - 2y)k̂ (C)</p> Signup and view all the answers

What are the parametric equations for the circle C with center at the origin and radius 3?

<p>x = 3 cos t, y = 3 sin t, z = 0 (D)</p> Signup and view all the answers

How is the work done in moving a particle expressed mathematically?

<p>$W = \int_C F~ · d~r$ (C)</p> Signup and view all the answers

What is the resulting expression for F~(r(t)) during the calculation of work?

<p>(6 cos t - 3 sin t)î + (3 cos t + 3 sin t)ĵ + (9 cos t - 6 sin t)k̂ (B)</p> Signup and view all the answers

What is the derivative of r(t) with respect to t?

<p>-3 sin tî + 3 cos tĵ (C)</p> Signup and view all the answers

How is the work calculated over the interval from 0 to $2\pi$?

<p>$\int_0^{2\pi} (9 - 9 cos t sin t) dt$ (B)</p> Signup and view all the answers

What is the final result for the work done after completing the calculations?

<p>$18\pi$ units (B)</p> Signup and view all the answers

Which trigonometric identity simplifies the expression $\int_0^{2\pi} cos t sin t dt$ in the calculations?

<p>$\int_0^{2\pi} \frac{1}{2} sin(2t) dt$ (D)</p> Signup and view all the answers

What aspect of the curve C is critical for defining the work done in a force field?

<p>The orientation and smoothness of the curve (D)</p> Signup and view all the answers

What does the term 'work' specifically refer to in this context?

<p>The energy transferred by a force (C)</p> Signup and view all the answers

What is the line integral of a vector function F over a curve C defined parametrically as r(t) from a to b?

<p>$\int_a^b F(r(t)) \cdot r'(t) , dt$ (B)</p> Signup and view all the answers

Given the vector field F = (3x^2 + 6y)î - 14yz ĵ + 20xz^2 k̂, what expression represents F evaluated at r(t)?

<p>$9t^2 î - 14t^5 ĵ + 20t^7 k̂$ (D)</p> Signup and view all the answers

How do you differentiate r(t) = tî + t^2 ĵ + t^3 k̂ with respect to t?

<p>$î + 2tĵ + 3tk̂$ (D)</p> Signup and view all the answers

What is the dot product result of F(r(t)) with r'(t) if F(r(t)) = 9t^2 î - 14t^5 ĵ + 20t^7 k̂ and r'(t) = î + 2tĵ + 3t^2 k̂?

<p>$9t^2 - 28t^6 + 60t^9$ (B)</p> Signup and view all the answers

If you evaluate the definite integral of 9t^2 - 28t^6 + 60t^9 from 0 to 1, what is the result?

<p>$5$ (C)</p> Signup and view all the answers

From the expression $F(r(t)) = 9t^2 î - 14t^5 ĵ + 20t^7 k̂$, what is the coefficient of the ĵ component?

<p>$-14t^5$ (B)</p> Signup and view all the answers

What parametric equation represents a straight line segment from (x0, y0, z0) to (x1, y1, z1)?

<p>$x = (1 - t)x_0 + tx_1$, $y = (1 - t)y_0 + ty_1$, $z = (1 - t)z_0 + tz_1$ (C)</p> Signup and view all the answers

What is the value of vector field F evaluated at the origin (0,0,0)?

<p>(0, 0, 0) (C), (0, 0, 0) (D)</p> Signup and view all the answers

In the context of vector calculus, what does the differential element d~r represent?

<p>An infinitesimal vector along the curve C in the parameterized form (C)</p> Signup and view all the answers

What does the term piecewise smooth curve refer to in the context of line integrals?

<p>A curve that consists of multiple smooth segments (A)</p> Signup and view all the answers

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Study Notes

Vector Equations of a Particle

  • Particle moves along a curve defined by ( x = t^2 ), ( y = -t^3 ), ( z = t^4 ).
  • Position vector is represented as ( \mathbf{r}(t) = t^2 \hat{i} - t^3 \hat{j} + t^4 \hat{k} ).

Velocity and Acceleration

  • Velocity ( \mathbf{v} ) is calculated as ( \frac{d\mathbf{r}}{dt} = 2t \hat{i} - 3t^2 \hat{j} + 4t^3 \hat{k} ).
  • Acceleration ( \mathbf{a} ) is calculated as ( \frac{d\mathbf{v}}{dt} = 2 \hat{i} - 6t \hat{j} + 12t^2 \hat{k} ).
  • At ( t = 1 ), ( \mathbf{v} = 2 \hat{i} - 3 \hat{j} + 4 \hat{k} ) and ( \mathbf{a} = 2 \hat{i} - 6 \hat{j} + 12 \hat{k} ).

Example of a Moving Particle

  • A particle moves with ( x = e^{-t} ), ( y = 2 \cos(3t) ), ( z = 2 \sin(3t) ).
  • Requires finding velocity and acceleration at any time.
  • Velocity and acceleration depend on differentiating the position equations.

Gradient of a Function

  • The gradient ( \nabla \phi ) of a function ( \phi = xyz ) includes derivatives with respect to ( x ), ( y ), and ( z ).
  • At the point ( (1, -1, 2) ), the gradient is ( -2 \hat{i} + 2 \hat{j} - \hat{k} ).

Magnitude of Gradient

  • For ( \phi = x^2 + y^2 + z^2 + 2xyz ), the gradient is ( \nabla \phi = (2x + 2yz, 2y + 2xz, 2z + 2xy) ).
  • At ( (2, -1, 1) ), the gradient evaluates to ( 2 \hat{i} + 2 \hat{j} - 2 \hat{k} ).
  • Magnitude is calculated as ( |\nabla \phi| = \sqrt{2^2 + 2^2 + (-2)^2} = 2\sqrt{3} ).

Divergence and Curl

  • Given ( \phi = 2x^3 y^2 z^4 ), the vector field ( \mathbf{F} = \nabla \phi ) involves partial derivatives.
  • Divergence ( \text{div} \mathbf{F} ) and curl ( \text{curl} \mathbf{F} ) are also calculated at the point ( (1, -1, 1) ).
  • ( \text{div} \mathbf{F} = 40 ) and ( \text{curl} \mathbf{F} = \mathbf{0} ).

Line Integral

  • Line integral of vector field ( \mathbf{F} ) along curve ( C ) defined parametrically involves the differential ( d\mathbf{r} ).
  • Example illustrates how to compute ( \int_C \mathbf{F} \cdot d\mathbf{r} ).

Work Done in a Force Field

  • Work done to move a particle along a defined path ( C ) in a force field ( \mathbf{F} ) is given by the line integral.
  • Sample calculation shows the process of applying the definitions and evaluating ( \int_C \mathbf{F} \cdot d\mathbf{r} ).
  • Required work done in moving a particle once around a circle with radius 3 is ( 18\pi ) units.

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