DAY 29

WARM-UP

A two-stage rocket accelerates from rest at +4.00m/s2 for 10.0 seconds. It then accelerates at +3.00 m/s2 for another 7.00 seconds. After the second stage, it enters into a state of free fall. 

A. When would the maximum speed occur, Stage 1 or Stage 2? 

B. Being careful to separate them into Stage 1 and Stage 2, write the Givens and Unknown for the problem.

C. Which equation would you use to find the maximum velocity at the end of stage 2?

CLASSWORK

1. #029A: Quiz 6: UAM Problem Solving

2. #029B: Multi-Stage Practice Problems

1. A two-stage rocket accelerates from rest at +4.00m/s2 for 10.0 seconds. It then accelerates at +3.00 m/s2 for another 7.00 seconds. After the second stage, it enters into a state of free fall.

2. A. When would the maximum speed occur, Stage 1 or Stage 2?

3. B. Determine the maximum speed.

4. A two-stage rocket accelerates from rest at +3.57 m/s2 for 6.82 seconds. It then accelerates at +2.98 m/s2 for another 5.90 seconds. After the second stage, it enters into a state of free fall.

5. A. Determine the maximum speed

6. B. Determine the maximum altitude.

    **The solution to problem #2 is here (it's #48 on the link): https://www.physicsclassroom.com/reviews/1D-Kinematics/Kinematics-Review-Answers-4

#028A (continued): Two-Stage Acceleration

    Handout: (it's on Schoology "Two Stage Rocket")

    Interactive Activity: LINK

Learning at Home (HW)

1. #029C: Review Free Fall

Take Notes: LINK 1

Watch the video, and answer the EdPuzzle Questions: LINK 2

#Goals: SWBAT...

1. Draw correct FBD's, with appropriate vector magnitude and direction.

2. Support classmates with helpful tutoring

3. Use FBD's to find Net Force

4. Describe the relationship between mass, net force, and acceleration

Warm-Up (4min) 

read the scenario below, then answer the questions at the end

Two students are discussing their physics homework prior to class. They are discussing an object that is being acted upon by two individual forces (both in a vertical direction); the free-body diagram for the particular object is shown at the right. During the discussion, Anna Litical suggests to Noah Formula that the object under discussion could be moving. In fact, Anna suggests that if friction and air resistance could be ignored (because of their negligible size), the object could be moving in a horizontal direction. According to Anna, an object experiencing forces as described at the right could be experiencing a horizontal motion as described below in a dot diagram  

Noah Formula objects, arguing that the object could not have any horizontal motion if there are only vertical forces acting upon it. Noah claims that the object must be at rest, perhaps on a table or floor. After all, says Noah, an object experiencing a balance of forces will be at rest. Who do you agree with? WHY?

CLASSWORK

1. #029A: FBD Quiz

2. Review the HW

4. Suppose that a sled is accelerating at a rate of 2 m/s2. If the net force is tripled and the mass is halved, then what is the new acceleration of the sled?

3. #029B: Finding Acceleration via FBD's

The net force is the vector sum of all the individual forces. 

In this lesson, we will learn how to determine the acceleration of an object if the magnitudes of all the individual forces are known. 

The three major equations that will be useful are 

the equation for net force (Fnet = m•a), 

the equation for gravitational force (Fg = m•g), 

and the equation for frictional force (Ff = μ • FN).   <------THIS IS NEW! :-)

The process of determining the acceleration of an object demands that the mass and the net force are known. If mass (m) and net force (Fnet) are known, then the acceleration is determined by use of the equation.

a = Fnet / m

Your Turn to Practice

Thus, the task involves using the above equations, the given information, and your understanding of Newton's laws to determine the acceleration. To gain a feel for how this method is applied, try the following practice problems. ALWAYS START BY SUMMING THE FORCES IN THE X and Y.

Practice #1

An applied force of 50 N is used to accelerate an object to the right across a frictional surface. The object encounters 10 N of friction. Use the diagram to determine the normal force, the net force, the mass, and the acceleration of the object. (Neglect air resistance.)