Query 21

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course PHY 201

4/19 about 4:55 pm

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:

We know that v_0_x will be the same throughout the fall. We also know that v_0_y = 0 m/s.

We can use the fourth equation and plug in v_0y = 0 and ‘ds along with a=g to find v_fy.

We now know v_fx and v_fy.

V_mag = ‘sqrt(v_fx^2 + v_fy^2)

‘theta = arctan (v_fy / v_fx), since v_fy will be negative, it will lie in the fourth quadrant and will get a negative result, between 0 and 90 deg. We must add 360 deg to account for this so that we will have a positive angle with the positive x axis.

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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:OK

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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 block starting at the origin with a force applied to it at 60 deg will be the same as a vertical force that equals F_mag * sin 60 deg. and a horizontal force that equals F_mag * cos 60 deg.

A collision in which you know the momentum of two objects moving in different directions. You could find the x and y components of these object’s momentums and thus the resultant momentum after collision. This would help you to find the velocity post collision of one of the objects if you know the post collision velocity of the other object along with the mass of the objects.

A third would be dealing with velocities of projectiles. If we know v_0x of an object rolling off a table, along with either ‘ds or ‘dt, we know that v_0x will also be v_fx, we can find v_fy with this information. This will allow us to find the mag. of the velocity at impact with the ground or at any point, given ‘ds or ‘dt, and also the angle of the velocity at that instant using arctan(v_0y / v_0x).

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):OK

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Self-critique Rating:OK

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&#Very good responses. Let me know if you have questions. &#