Homework

- Reading Preparation
- Key Equations
- WebLecture
- Study Activity
- Chat Preparation Activities
- Chapter Quiz
- Lab Work

**Text Reading**: Giancoli, *Physics - Principles with Applications*, Chapter 3: Sections 5-8

*Section 5:*Vectors at right angles do not affect one another. The horizontal components (unaffected by gravity) of a projectile's motion do not affect the vertical components (which are subject to gravitational acceleration), so we can analyze them separately.*Section 6:*In working with projectile problems, always try to break the problem apart into vertical and horizontal components of motion (displacement, velocity, acceleration). Select your origin and frame of reference to make the math simple, and use it consistently. To get the final summary solution, add the horizontal and vertical vectors back together.*Section 7:*Note that motion of a projectile is parabolic and described by the quadratic equation, so we can use the mathematical tools we know for quadratics to specific projectile situations.*Section 8:*Velocity is measured based on a frame of reference. An observer on a roadside uses a different frame of reference (and sees a different velocity) than an observer in a moving vehicle. To compare velocities, we have to know the difference in the velocities of the*frames of reference*. An important law of physics is that as long as neither frame is accelerating, the laws of physics will be the same in both frames.

The Range Equation for Projectiles (where y = y_{0})
$$R\text{}=\text{}\frac{{{v}_{0}}^{2}\text{}\mathrm{sin}\text{}2{\theta}_{0}}{g}$$

Note that when θ_{0} = 45°, sin 2θ = sin 90° = 1, and has the maximum value possible for any θ,
$$R\text{}=\text{}\frac{{{v}_{0}}^{2}\text{}}{g}$$

Projectile Motion is Parabolic $$y\text{}=\text{}\frac{{v}_{\mathrm{y0}}}{{v}_{\mathrm{x0}}}\text{}x\text{}-\text{}(\frac{g}{2{{v}_{\mathrm{x0}}}^{2}}){x}^{2}$$

**Read the following weblecture before chat**: Unit Vector notation

The website below will either download a Java applet to your computer or run the applet in place, depending on how your browser is configured. You will need Java installed to run the applet locally on your computer.

The "projectile motion" simulation allows you experimnt with projectiles launched at different speeds and angles. Use the slide bar to adjust the initial speed. Grab the mouth of the cannon to tilt it to different angles. Use the red cannon button to fire the cannon and the eraser button to reset. See if you can find more than one combination to hit the bull's eye (three stars).

- With the vectors panel, turn the different components on and off to identify the velocity and acceleration vectors involved, and watch how they change as the projectile ascends and descends. Are velocity and acceleration always in the same direction? Are acceleration and force always in the same direction?
- We'll come back to this scenario to see how drag force affects projectile motion in the next chapter.

Physics simulation Java Applets are the product of the PHET Interactive Simulations project at the University of Colorado, Boulder.

**Forum question**: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer**before**chat starts for this session.**Mastery Exercise**: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.

**Required**: Complete the Mastery exercise with a passing score of 85% or better.- Go to the Moodle and take the quiz for this chat session to see how much you already know about astronomy!

If you want lab credit for this course, you must complete at least 12 labs (honors course) or 18 labs (AP students). One or more lab exercises are posted for each chapter as part of the homework assignment. We will be reviewing lab work at regular intervals, so do not get behind!

**Lab Instructions**: Velocity of Falling Bodies 2

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