Query Questions 21

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course Phy 241

November 7 around 7:30pm.

021. `query 21*********************************************

Question: `q Explain how to obtain the final speed and direction of motion of a projectile which starts with known velocity in the horizontal direction and falls a known vertical distance, using the analysis of vertical and horizontal motion and vectors.

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Your solution:

Vo_y=0

Downward acceleration of 9.807cm/s^2 or 32.2ft/s^2

Vf^2=v0^2+2a’ds

After knowing x and y components, you can use the pythag thm to find speed and arctan (y/x) to find direction.

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Given Solution:

`a** The horizontal velocity is unchanging so the horizontal component is always equal to the known initial horizontal velocity.

The vertical velocity starts at 0, with acceleration thru a known distance at 9.8 m/s^2 downward. The final vertical velocity is easily found using the fourth equation of motion.

We therefore know the x (horizontal) and y (vertical) components of the velocity. Using the Pythagorean Theorem and arctan (vy / vx) we find the speed and direction of the motion. **

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Self-critique (if necessary):

OK, should’ve mentioned that the horizontal velocity is unchanging, therefore the x component=known vo_x.

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self-critique rating #$&*:

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Question: `qGive at least three examples of vector quantities for which we might wish to find the components from magnitude and direction. Explain the meaning of the magnitude and the direction of each, and explain the meaning of the vector components.

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Your solution:

A football thrown across the field with speed of “u” at an angle (theta).

ux=u cos(theta)

uy=u sin(theta)

vy=uy-at

final vertical velocity at max height will be 0

t=uy/a

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Given Solution:

`a

Examples might include:

A force acting on an object causing it to move in an angular direction.

A ball falling to the ground with a certain velocity and angle.

A two car collision; velocity and momentum are both vector quantities and both important for analyzing the collision..

The magnitude and directiohn of the relsultant is the velocity and direction of travel.

The vector components are the horizontal and vertical components that would produce the same effect as the resultant.

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Self-critique (if necessary):

OK, had the main idea down, just didn’t specify what the magnitude, direction, and vector components actual MEANT.

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self-critique rating #$&*:

&#This looks good. Let me know if you have any questions. &#

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