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# The Rock Problem

Lesson 10 of 13

## Objective: SWBAT relate first and second derivatives to velocity and acceleration.

*50 minutes*

#### Launch and Explore

*25 min*

I love today's lesson! **First and second derivatives can be very abstract to students and today we give them meaning** and students are presented with a context that make them seem very real. Today's lesson start by giving students this worksheet and having them work on it with their table group. It is rather lengthy, so I want to give them plenty of time to work on it and digest the concepts.

While they are working, there are a few key ideas that I watch out for. I want to make sure that students are on the right track and are not getting tripped up by simple ideas. Here are a few things that I monitor:

**Average velocity**: For questions #1-5, student must find the average velocity over a specific interval. If students get stuck, I ask them how we measure velocity to remind them that we just calculate distance divided by time.**Understanding instantaneous velocity**: Students may not understand this concept, so I liken it to when a police officer clocks someone using a radar gun - it is the speed at precisely one instant (theoretically).**Calculating the instantaneous velocity**: I don't expect all students to figure out #6, but I at least hope they can see that as the interval gets smaller, we are approaching a better estimate to the instantaneous velocity.**Finding the velocity at the highest point**: It may seem strange to students that velocity can be zero when the rock is at the highest point, but the rock must stop at some point when switching directions.**The first derivative**: If students do not pick up on the fact that the first derivative is giving velocity, then I ask them to decide what unit the function is measured in to see if that will help.

#### Resources

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#### Share

*20 min*

To being our discussion we go through our answers to questions #1-5 from the worksheet and I choose one student to explain their process to the class. I make sure that during our discussion, students understand that we really **used the slope formula to figure out the average velocity**. When it comes time to answer #6, it will hopefully be clear that we need to find the slope of the tangent line at *t* = 1.

The questions on the back are a little more involved. In the videos below I **highlight some key points and suggestions** I make when discussing some of these questions.

**#8 - The derivative of the position function: **

**#9 - The second derivative of the position function:**

**#10 - Finding the time when the speed of the rock is 30 feet per second:** Make sure that students realize that the speed is 30 feet/sec when the velocity is 30 feet/sec* or *-30 feet/sec. Thus, the rock will hit 30 feet/sec on the way up and on the way down.

#### Resources

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#### Summarize

*5 min*

This lesson is always demanding, but I find that my students seem to be** really engaged and we have some great discussions**. To close the lesson, I ask students to think about the following to summarize everything that we learned:

- How are the position function, velocity function, speed function and acceleration function related?
- For each of the position, velocity, and acceleration functions, what is x-axis measuring? The y-axis?

Finally, here is a homework assignment to reinforce the work we did with velocity and acceleration.

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- UNIT 1: Functioning with Functions
- UNIT 2: Polynomial and Rational Functions
- UNIT 3: Exponential and Logarithmic Functions
- UNIT 4: Trigonometric Functions
- UNIT 5: Trigonometric Relationships
- UNIT 6: Additional Trigonometry Topics
- UNIT 7: Midterm Review and Exam
- UNIT 8: Matrices and Systems
- UNIT 9: Sequences and Series
- UNIT 10: Conic Sections
- UNIT 11: Parametric Equations and Polar Coordinates
- UNIT 12: Math in 3D
- UNIT 13: Limits and Derivatives

- LESSON 1: The Limit of a Function
- LESSON 2: Techniques for Finding Limits
- LESSON 3: The Tangent Line Problem - Day 1 of 2
- LESSON 4: The Tangent Line Problem - Day 2 of 2
- LESSON 5: The Power Rule
- LESSON 6: Formative Assessment: Limits and Derivatives
- LESSON 7: Derivatives and Graphs
- LESSON 8: The Second Derivative
- LESSON 9: Maximizing Volume - Revisited
- LESSON 10: The Rock Problem
- LESSON 11: Unit Review: Limits and Derivatives
- LESSON 12: Unit Review Game: The Row Game
- LESSON 13: Unit Assessment: Limits and Derivatives