PHYS-UA 11 Lecture Notes - Lecture 1: Coordinate Space, Cross Product, Negative Number

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10 Sep 2016

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Physics: lecture 1 (vectors): a vector has both a, magnitude, direction, vectors on a coordinate scale can be represented by three entities: , j, k, to represent the x,axis, y-axiz, and z-axis, respectively, coordinates: Vector a = 3 : if you multiply a vector by -1, you essentially reverse its direction, specifying direction: vectors having the same direction are parallel to each other. Vector b = 4 -4j: vector addition and subtraction: The starting point of a vector on a grid is arbitrary. Express the vector in terms of , j and k, irrelevant of where the origin is. A vector that is 3 at (0,0) is identical to a vector that is 3 at (1,1). To add vectors (and subtract them), simply add their components. Add the components of the two vectors, then the j, and k. Move vectors so as to join them tip to tail without changing their orientation.

Related Questions

(A) Show that the position of a particle on a circle of radius Rwith center at the origin (x=0,y=0) is given in unit vectors byr=cosÎ¸i+sinÎ¸j, where Î¸ is the angle of the position vector with thex axis.

B) If the particle moves with constant speed v and period T,starting on the x axis at t=0, find an expression for Î¸ in terms ofthe time and T.

C) Differentiate the position vector twice with respect to timeto find the acceleration and show that it is the centripetalacceleration, whose magnitude is given by equation (a=(v^2)/r) andwhose direction is toward the center of the circle. (Not that theunit vectors i and j are constants, independent of time.)

A force F⃗ of magnitude F making an angle θ with the x-axis is applied to a particle located along the axis of rotation A, at Cartesian coordinates (0,0) in the figure. The vector F⃗ lies in the XY plane, and the four axes of rotation A, B, C, and D all lie perpendicular to the XY plane. (Figure 1)

A particle is located at a vector position r⃗ with respect to an axis of rotation (thus r⃗ points from the axis to the point at which the particle is located). The magnitude of the torque τ about this axis due to a force F⃗ acting on the particle is given by

τ=rFsin(α)=(moment arm)⋅F=rF⊥,

where α is the angle between r⃗ and F⃗ , r is the magnitude of r⃗ , F is the magnitude of F⃗ , the component of r⃗ that is perpendicular to F⃗ is the moment arm, and F⊥ is the component of the force that is perpendicular to r⃗ .

Sign convention: You will need to determine the sign by analyzing the direction of the rotation that the torque would tend to produce. Recall that negative torque about an axis corresponds to clockwise rotation.

In this problem, you must express the angle α in the above equation in terms of θ, ϕ, and/or π when entering your answers. Keep in mind that π=180degrees and (π/2)=90 degrees.

Part A

What is the torque τA about axis A due to the force F⃗ ?

Express the torque about axis A at Cartesian coordinates (0,0).

τA =

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Part B

What is the torque τB about axis B due to the force F⃗ ? (B is the point at Cartesian coordinates (0,b), located a distance b from the origin along the y axis.)

Express the torque about axis B in terms of F, θ, ϕ, π, and/or other given coordinate data.

τB =

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Part C

What is the torque τC about axis C due to F⃗ ? (C is the point at Cartesian coordinates (c,0), a distance c along the x axis.)

Express the torque about axis C in terms of F, θ, ϕ, π, and/or other given coordinate data.

τC =

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Part D

What is the torque τD about axis D due to F⃗ ? (D is the point located at a distance d from the origin and making an angle ϕ with the x axis.)

Express the torque about axis D in terms of F, θ, ϕ, π, and/or other given coordinate data.

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This print-out should have 15 questions. Multiple-choice questions may continue on the next column or page - find all choices before answering. Two vectors A and B lie in the xy plane and are given by A = Ax i + Ay j B = Bx i + By j, where Ax = 3.58 m, Ay = 2.85 m, Bx = 7.09 m, By = -6.36 m. Find the magnitude of R = A + B. Answer in units of m Find the angle theta (between -180 degree and + 180 degree with counterclockwise positive) that the vector R makes from the positive x axis. Answer in units of degree When the Sun is directly overhead, a hawk dives toward the ground at a speed of 7.23 m/s. If the direction of his motion is at an angle of 39.8 below the horizontal, calculate the speed of his shadow along the ground. Answer in units of m/s Vector A has a magnitude of 10 and points in the positive x-direction, Vector B has a magnitude of 17 and makes an angle of 32 degree with the positive x-axis. What is the magnitude of A - B? An airplane starting from airport A (lies 342 km east, then 531 km at 62.2 degree west of north, and then 778 km north to arrive finally at airport B. The next day, another plane flies directly from A to B in a straight line. In what direction should the pilot trawl in this direct flight? Use counterclockwise its the positive angular direction from due east, between the limits of - 180 degree ami 180 degree . Assume there is no wind during these flights. Answer in units of degree How far will the pilot travel in this direct flight? Answer in units of km A projectile is fired straight upward at 126 m/s. How fast is it moving at the instant it reaches the top of its trajectory? Answer in units of m/s How fast is it moving at the instant it reaches the top of its trajectory if the projectile is fired upward at 12 degree from the horizontal? Answer in units of m/s At one instant the velocity of a particle is and a very short time later its velocity has changed to . Qualitatively, what was the direction of the particle's acceleration during the interval between the first and second instance?

PHYS-UA 11 Lecture Notes - Lecture 1: Coordinate Space, Cross Product, Negative Number

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