Query 21

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course PHY 121

7/25 12:30

021. `query 21

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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:

The final x velocity is the horizontal velocity that is given because it does not

accelerate.

The final y velocity is the displacement times -9.8 m/s^2 because the force of gravity

is pulling down on the object, which is in a negative direction on the ""grid.""

The magnitude of the final speed is the square root of the final x velocity squared plus

the square root of the final y velocity squared.

The angle is tan-1 (final y velocity/final x velocity).

confidence rating #$&*:

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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

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Self-critique Rating: 2

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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:

Velocity: A projectile goes horizontally and vertically. You end up with a right angle. The x side is the horizontal velocity. The y side shows the vertical velocity. The hypotenuse shows the magnitude of those velocity vectors. You can find the direction by finding the angle.

Displacement: A projectile goes horizontally and vertically. You end up with a right angle. The x side is the horizontal displacment. The y side is the vertical displacement. The hypotenuse shows the magnitude of those displacement vectors. The angle tells the direction of the displacement.

Force: Two forces are acting on an object. One is horizontal and the other is vertical. Sometimes they aren't, but you can rotate the grid to make it so. The horizontal force would be shown on the x axis. The vertical force would be shown on the y axis. By combining those vectors, you can find out the total force on the object and in what direction it moves. The hypotenuse gives you the total force and the angle gives you the direction.

confidence rating #$&*:

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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):

I guess I wasn't specific enough with examples.

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Self-critique Rating: 2

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