Physics - Analyzing 1 Dim Motion (con't)

OPENING QUESTION:

Let's revisit my expectation for isolating variables.

Remember, I don't want you to worry about showing the various steps you might need to take to isolate a particular variable. For right now, if it is helpful for you to break those down into steps you are welcome to do that, but that is neither requested or required since that tends to just clutter up the page.

For example, consider the following equation:

5x + 4a + 5c = 110

Isolate for a:

a = (110 -5x - 5c) / 4

That's all the detail I need or want to see.

So let's say that you know everything about an object's motion (initial displacement, final displacement, acceleration and time) *EXCEPT* it's initial velocity.

Write the honker down (let's say it is vertical motion), and isolate for vi

 

LEARNING OBJECTIVES:

  • I will be able to determine if a 1 dim problem is horizontal motion or vertical motion *AT A GLANCE* during today's class.

CALENDAR: UNIT TEST ON THURSDAY -- Motion in 1 dim

WORDS O' THE DAY:

  • gravity! gravity! gravity!

FORMULAE OBJECTUS:

    • a = (vf - vi)/(tf - ti) (definition of acceleration)

    • g = 9.81 m/s2 (acceleration an object experience on Earth) ONLY present in vertical motion (Y axis) problems

horizontal motion:

    • 1) vavg (vf + vi )/2
    • 2) vf = vi +at
    • 3) xf = xi + vit + 1/2at2
    • 4) vf2 - vi2 = 2a∆x

vertical motion:

      • 1) vavg = (vf + vi )/2
      • 2) vf = vi + ag t
      • 3) yf = yi + vit + 1/2ag t2
      • 4) vf2 - vi2 = 2a∆y

WORK O' THE DAY:

I asked you to setup the beetle racing problem in the Physics Classroom - Let's go take a look at the Beetle Problem #31

Please share your sketch and initial conditions with your team. Verify all initial conditions are present whether stated or implied.

Remember, this is a horizontal motion problem so Ag doesn't apply.

 

Notice that problem #31 uses average velocity, that means acceleration goes away since all we know is that each beetle is moving at the same velocity during its entire 'run'.

How does my example above relate to this problem? Please discuss.

Oh and try dropping that problem into chatGpt. Just cuz ... <uh oh!>

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Imagine you are in outer space in the brand new shuttle that your folks were kind enough to lend you for the day. You're coasting along at a fairly mellow 95 m/s. Just for fun you hit the 'go' button and you suddenly accelerate at a rather uncomfortable 6.5 m/s/s. How much has your position changed after 19.24 seconds?

Why is it significant that this problem occurs in space?

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Now imagine we're back on Earth. You launch a frozen grape upwards with a fairly brisk initial velocity of 59.12 m/s. Where is the grape after 9.15 seconds. Please sketch and label all initial conditions.

Discuss with your team a method to break that problem into an on-the-way-up and on-the-way-down problem.

Now discuss doing it in one.

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Now we'll get a bit more feisty. At what time is that grape at 100. meters? Why is that a particularly sly question?

We can do it in one, in fact we BETTER do it in one. Why?