query assignment 19

course phy201

Where in the assignments, other than the experiment completed back in assignment 12, did we cover projectile motion?

Projectiles are covered in Class Notes #15 and 21 (and at least one other set of notes in between), and in Introductory Problem Set 4.

^ˆ¯FvÁÓ½¼»ä¬éÞjÚ¯©š¥TáÄ÷Lßçø…¯©assignment #019

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019. `query 19

Physics I

10-23-2007

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13:41:09

Query class notes #20

Explain how we calculate the components of a vector given its magnitude and its angle with the positive x axis.

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RESPONSE -->

The magnitude is the hyp of the right triangle formed by the X and Y components of the vector. Knowing this and the angle we can use trig to calculate the length or magnitude of the X and Y components using the sine and cosine functions.

confidence assessment: 3

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13:41:24

** STUDENT RESPONSE:

x component of the vector = magnitude * cos of the angle

y component of the vector = magnitude * sin of the angle

To get the magnitude and angle from components:

angle = arctan( y component / x component ); if the x component is less than 0 than we add 180 deg to the solution

To get the magnitude we take the `sqrt of ( x component^2 + y component^2) **

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RESPONSE -->

self critique assessment: 3

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13:44:08

Explain what we mean when we say that the effect of a force is completely equivalent to the effect of two forces equal to its components.

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RESPONSE -->

Unless a force is applied directly parallel it will have some component in the Y direcion and some compnent in the X direction. When combining the effect of these two forces we understand the effect of the total force.

confidence assessment: 2

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13:44:25

** If one person pulls with the given force F in the given direction the effect is identical to what would happen if two people pulled, one in the x direction with force Fx and the other in the y direction with force Fy. **

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RESPONSE -->

self critique assessment: 2

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13:46:17

Explain how we can calculate the magnitude and direction of the velocity of a projectile at a given point.

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RESPONSE -->

There are two forces at work. One is horizontal (X) and the other vertical (Y). By studying the separate effect of each of these comp0nents we can understand the direction and velocity of the projectile.

confidence assessment: 2

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13:49:05

** Using initial conditions and the equations of motion we can determine the x and y velocities vx and vy at a given point, using the usual procedures for projectiles.

The magnitude of the velocity is sqrt(vx^2 + vy^2) and the angle with the pos x axis is arctan(vy / vx), plus 180 deg if x is negative. **

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RESPONSE -->

I had not been exposed to these formulas before I don't think. Probably found in chapter 3. Or maybe class notes? elsewhere? Not sure.

self critique assessment: 1

check out the class notes, especially #21, if I recall correctly.

The general principle:

Analyze the vertical and horizontal motions independently (with `dt the only common quantity).
If you know vx and vy you can use the general principles of vectors to find the magnitude and angle of the resultant velocity.

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13:55:56

Explain how we can calculate the initial velocities of a projectile in the horizontal and vertical directions given the magnitude and direction of the initial velocity.

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RESPONSE -->

In the horizontal direction velocity is constant and in the vertical direcion it accelerates at the rate of gravity. The velocity at any given point is a combination of these two vector velocities.

confidence assessment: 1

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13:56:26

** Initial vel in the x direction is v cos(theta), where v and theta are the magnitude and the angle with respect to the positive x axis.

Initial vel in the y direction is v sin(theta). **

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RESPONSE -->

don't understand this yet.

self critique assessment: 1

The x and y components of a vector quantity are the products of the magnitude of the vector and, respectively, the cosine and the sine of the angle as measured counterclockwise from the positive x axis.

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See my notes; be sure to see the indicated Class Notes. I think this will clarify the projectile questions. Let me know if you have additional questions.