PHYSICS 2020 - 21 December 7, 2020

Today’s Agenda (Day 74)

1. HOMEWORK CHECK Chapter 10 Vocabulary Mini-Project: Racecar Report

2. CLASS ACTIVITY BEGIN: Chapter 10 PPT Review

a) Section 1 – Work & Energyb) Section 2 - Machines

HOMEWORK: READ: Chapter 10 – Energy, Work & Simple Machines COMPLETE: Chapter 10 Notes STUDY: Chapter 10Testhttp://glencoe.mheducation.com/sites/0078807220/student_view0/self-check_quizzes.html

Chapter 9 – Momentum and Its ConservationImpulse Angular momentum Isolated systemMomentum Angular impulse-angular

momentum theoremLaw of conservation of angular momentum

Impulse-momentum theorem

Closed system Law of conservation of momentum

Chapter 10 – Energy, Work & Simple MachinesWork Work-energy

theoremTranslational kinetic energy

Mechanical advantage

Ideal mechanical advantage

Joule Kinetic energy Machine Effort force EfficiencyEnergy power Watt Resistance force Compound

machine

REMINDERS: ?QUIZ: Chapter 9 & 10 Vocabulary Dec. 9 TEST: Chapter 10 December 10 Chapter 10 Vocabulary – Dec. 5 Chapter 10 Notes – Dec. 8

Mousetrap Racer Challenge: Due DatesNov. 23 – Drawing #1 Dec. 2 – Test RacerNov. 30 – Construct Racer Dec. 5 - CompetitionDec. 1 – Drawing #2 Dec. 7 – Mini- Project Report

PHYSICS 2020 – 21 SECTION REVIEW

PRACTICE PROBLEMS 10.1

1. Together, two students exert a force of 825 N in pushing a car a distance of 35 m. a) How much work do the students do on the car?b) If their force is doubled, how much work must they do on the car to push it the

same distance?

2. A rock climber wears a 7.5 kg backpack while scaling a cliff. After 30.0 min, the climber is 8.2 m above the starting point.a) How much work does the climber do on the backpack?b) If the climber weighs 645 N, how much work does she do lifting herself and the

backpack?

3. Two people lift a heavy box a distance of 15 m. they use ropes, each of which makes an angle of 15◦ with the vertical. Each person exerts a force of 225 N. How much do the ropes do?

4. An airplane passenger carries a 215 N suitcase up the stairs, a displacement of 4.20 m vertically and 4.60 m horizontally.a) How much work does the passenger do on the suitcase?b) The same passenger carries the same suitcase back down the same set of stairs.

How much work does the passenger do on the suitcase to carry it down the stairs?

5. A rope is used to pull a metal box a distance of 15.0 m across the floor. The rope is held at an angle of 46.0 ◦ with the floor, and a force of 628 N is applied to the rope. How much work does the rope do on the box?

6. A 575 N box is lifted straight up a distance of 20.0 m by a cable attached to a motor. The box moves with a constant velocity and the job is done in 10.0 s. What power is developed by the motor in W and kW?

7. You push a wheelbarrow a distance of 60.0 m at a constant speed for 25.0 s by exerting a 145 N force horizontally.a) What power do you develop?b) If you move the wheelbarrow twice as fast, how much power is developed?

8. An electric motor develops 65 kW of power as it lifts a loaded elevator 17.5 m in 35 s. How much force does the motor exert?

PRACTICE PROBLEMS 10.21. A sledgehammer is used to drive a wedge into a log to split it. When the wedge is

driven 0.20 m into the log, the log is separated a distance of 5.0 cm. A force of 1.7 x 104 N is needed to split the log, and the sledgehammer exerts a force of 1.1 x 104 N.a) What is the IMA of the wedge?b) What is the MA of the wedge?c) Calculate the efficiency of the wedge as a machine.

2. A worker uses a pulley to raise a 24.0 kg carton 16.5 m, as shown in Figure 15 on p. 280 of the textbook. A force of 129 N is exerted, and the rope is pulled 33.0 ma) What is the MA of the pulley?b) What is the efficiency of the pulley?

3. A winch has a crank with a 45 cm radius. A rope is wrapped around a drum with a 7.5 cm radius. One revolution of the crank turns the drum one revolution. a) What is the ideal mechanical advantage of this machine?b) If, due to friction, the machine is only 75 percent efficient, how much force would

have to be exerted on the handle of the crank to exert 750 N of force on the rope?4. You exert a force of 225 N on a lever to raise a 1.25 x 103 N rock a distance of 13 cm.

If the efficiency of the lever is 88.7%, how far did you move your end of the lever?5. Classify each tool as a lever, a wheel and axle, an inclined plane, or a wedge.

Describe how it changes the force to make the task easier.a) Screwdriver c) chiselb) Pliers d) nail puller

6. A worker is testing a multiple pulley system to estimate the heaviest object that he could lift. The largest downward force he can exert is equal to his weight, 875 N. When the worker moves the rope 1.5 m, the object moves 0.25 m. What is the heaviest object he could lift?

7. Takeshi raises a 1200-N piano a distance of 5.00 m using a set of pulleys. He pulls in 20.0 m of rope.a) How much effort force would Takeshi apply if this were an ideal machine?b) What force is used to balance the friction force if the actual effort is 340 N?c) What is the output work?d) What is the input work?e) What is the mechanical advantage?

8. A motor with an efficiency of 88% runs a crane with an efficiency of 42 percent. The power supplied to the motor is 5.5 kW. At what constant speed does the crane lift a 410-kg crate?

PHYSICS 2020 – 21 ACTIVITY CHALLENGE

Overview: For this activity, you and the members of your group will compete in speed trials for various events: Scooter Sprint (SS), Scooter Agility (SA), Scooter Distance (SD), and Scooter Relay (SR). Distance and time measurements will be gathered and used to help determine the speed of each participant for each event.

Materials: • 1 gym scooter • 5 cones/markers • timer/smartphone with lap function • writing utensil • calculator

Procedures: 1. Set up the appropriate event course as detailed by specifications and the

teacher. 2. Sit on the scooter. Have one of your partners record how long it takes you to

complete the course. 3. Record the distance traveled and the amount of time taken to complete the

event course in the appropriate data table. 4. Calculate the speed of each group member by dividing the distance traveled by

the time and find the average speed for the group. 5. Repeat steps one through four with all members of the group, for each event

course (SS, SA, SD, SR).

The Scooter Games – Rules

1. Competitors must be seated on the scooter.

2. Competitors will be provided with a brief period of time to familiarize themselves with the scooter prior to the official start.

3. Prior to the official start of a timed trial, the front edge of the scooter must sit behind the start line.

4. The student timer must stand next to the finish line in order to get an accurate time measurement. The timer should be stopped once the entire scooter passes the finish line.

5. Competitors are not allowed to put their hands on the ground. Penalty – 10 seconds.

6. Competitors must not touch/hit any cone. Penalty – 5 seconds.

7. Competitors must always be facing and moving forward during a timed trial. Penalty – disqualification.

8. Competitors must go around every cone during a timed trial, with the exception of SS. Penalty – disqualification.

9. Competitors must remain on the scooter at all times during a timed trial. Penalty - disqualification.

10. Competitors cannot interfere with other competitors during a timed trial. Penalty - disqualification.

Event Courses - Specifications Scooter Sprint (1x)

Start Finish

10 meters

• Scooter Agility (1x)

• Scooter Distance (4x)

Start/ FinishFinish

10 meters

Scooter Relay (4 Competitors/Teammates – 1x each)

Start/ FinishFinish

10 meters

Data: Table 1 – Scooter Sprint (SS)

Member Distance (meter)

Time (second)

Speed Calculations

(distance ÷ time)

Speed (meter/second)

Average Speed =

Table 2 – Scooter Agility (SA) Member Distance

(meter) Time (second)

Speed Calculations

(distance ÷ time)

Speed (meter/second)

Average Speed =

Table 3 – Scooter Distance (SD)

Member Distance (meter)

Time (second)

Speed Calculations

(distance ÷ time)

Speed (meter/second)

Average Speed =

Table 4 – Scooter Relay (SR)

Leg Distance (meter)

Time (second)

Speed Calculations

(distance ÷ time)

Speed (meter/second)

1

2

3

4

Combined Legs (1-4)

Average Leg Speed =

General Questions (Group):

1. In what event did your group have the fastest average speed? What could have accounted for this? How does your speed compare to the group’s average speed for this event?

2. In what event did your group have the slowest average speed? What could have accounted for this? How does your speed compare to the group’s average for this event?

Scooter Games – Event Finals – Winner’s Data

Scooter Sprint

Distance (meter)

Time (second)

Speed Calculations (distance ÷ time)

Speed (meter/second)

Scooter Agility

Distance (meter)

Time (second)

Speed Calculations (distance ÷ time)

Speed (meter/second)

Scooter Distance

Distance (meter)

Time (second)

Speed Calculations (distance ÷ time)

Speed (meter/second)

Scooter Relay

Leg Distance (meter)

Time (second)

Speed Calculations

(distance ÷ time)

Speed (meter/second)

1

2

3

4

Combined Legs (1-4)

Average Leg Speed =

General Questions (Overall):

1. Using the SR data (from your group and the overall winning group), create a multiple line graph with time on the x-axis and distance on the y-axis. This is known as a distance-time graph. It will be necessary for you to graph the cumulative data for time and distance at 20 meter intervals. A table has been provided to help you organize your data.

Leg Your Group Winning Group

Time (s)

Plotted Time (s)

Distance (m)

Plotted Distance

Time (s)

Plotted Time (s)

Distance (m)

Plotted Distance

(m) (m)

1

2

3

4

2. Compare and contrast the line representing your group’s relay speeds with the overall winning group’s relay speeds.

3. What would the presence of a straight line on a distance-time graph indicate?

4. What would the presence of a positively sloped line on a distance-time graph indicate? A negatively sloped line?

5. What factors could have impacted the accuracy of the calculated speeds for this activity?

6. It is possible for an individual or group’s preliminary speed(s) to be faster than the overall winner’s speed. What could account for this?

Using the Speed Formula:

SHOW YOUR WORK!

1. Consider your group’s average speed for the SS and the overall winner’s speed.

a. How long would it take your group to travel a distance of 35 meters?

b. How long would it take the overall winner to travel a distance of 35 meters?

2. Consider your group’s average speed for the SA and the overall winner’s speed.

a. How far would your group travel if you moved on the scooter for 50 seconds?

b. How far would the overall winner travel if they moved on the scooter for 50 seconds?

3. Consider your group’s average speed for the SD and the overall winner’s speed.

a. How much longer would it take your group to travel a distance of 120 meters compared to the overall winner?

b. How much further would the overall winner travel in 5 minutes compared to your group?

Using the Acceleration Formula:

Although you never specified a direction with your calculated speeds for the Scooter Games, the speeds should be used when velocity is called for in all problems that follow.

SHOW YOUR WORK!

1. Consider your group members’ individual SS data and the overall winner’s SS data.

a. Calculate each group member’s acceleration.

b. Calculate the overall winner’s acceleration.

c. Compare and contrast each of your group member’s acceleration to one

another.

d. Compare and contrast each of your group member’s acceleration to the overall winner’s acceleration.

2. Consider your group’s SR data and the overall winning group’s SR data. a. What is your group’s acceleration for each leg (1-4) of the race?

Approach this as if there was never an exchange of the scooter between members of the group, and it was just a straight, 80m race. The information below will help guide you.

Show your work!

i. Leg 1

• Vi = 0 • Vf = average velocity for leg 1 • T = time to complete leg 1

ii. Leg 2 • Vi = average velocity for leg 1 • Vf = average velocity for leg 2 • T = time to complete leg 2

iii. Leg 3 • Vi = average velocity for leg 2 • Vf = average velocity for leg 3

• T = time to complete leg 3

iv. Leg 4 • Vi = average velocity for leg 3 • Vf = average velocity for leg 4 • T = time to complete leg 4

b. What is the overall winning group’s acceleration for each leg (1-4) of the race? Approach this as if there was never an exchange of the scooter between members of the group, and it was just a straight, 80m race.

Show your work!

i. Leg 1

• Vi = 0 • Vf = average velocity for leg 1 • T = time to complete leg 1

ii. Leg 2

• Vi = average velocity for leg 1 • Vf = average velocity for leg 2 • T = time to complete leg 2

iii. Leg 3 • Vi = average velocity for leg 2 • Vf = average velocity for leg 3 • T = time to complete leg 3

iv. Leg 4

• Vi = average velocity for leg 3 • Vf = average velocity for leg 4 • T = time to complete leg 4

3. Using the SR data (from your group and the overall winning group), create a multiple line graph with time on the x-axis and velocity on the y-axis. This is known as a velocity-time graph. It will be necessary for you to graph the cumulative data for the time. For example, if Leg 1 takes 10 seconds and Leg 2 takes 15 seconds, the second plotted time would be 25 seconds (10 seconds + 15 seconds). A table has been provided to help you organize your data.

Leg Your Group Winning Group Time (s) Plotted

Time (s) Velocity

(m/s) Time (s) Plotted

Time (s) Velocity

(m/s)

1

2

3

4

4. Compare and contrast the line representing your group’s acceleration with the one representing the overall winning group’s acceleration.

5. What would the presence of a straight line on a velocity-time graph indicate?

6. What would the presence of a positively sloped line on a velocity-time graph indicate? A negatively sloped line?

7. What factors could have impacted the accuracy of the calculated accelerations for this activity?

8. It is possible for an individual or group’s preliminary acceleration(s) to be greater than the overall winner’s acceleration(s). What could account for this?

9. Does a greater, positive, acceleration in the beginning of the race always result in a win? Explain your reasoning.

Using the Momentum Formula:

Complete the tables below with the mass of your group’s member and the mass of the overall event winners.

Group Member Mass (kg)

Event Winner Mass (kg)

Scooter Sprint

Scooter Agility

Scooter Distance

Scooter Relay

Leg 1 Racer

Leg 2 Racer

Leg 3 Racer

Leg 4 Racer

SHOW YOUR WORK!

1. Consider your group members’ individual SA data and the overall winner’s SA data.

a. Calculate each group member’s momentum.

b. Calculate the overall winner’s momentum.

c. Compare and contrast each of your group member’s momentum to one

another.

d. Compare and contrast each of your group member’s momentum to the overall winner’s momentum.

2. Consider your group member with the greatest momentum and your group member with the least momentum. Relative to each other, how did they fare during the SA race?

3. Consider the overall winner of the SA race. How does the overall winner’s momentum compare to your group member with the greatest momentum and your group member with the least momentum?

4. Do you think it is beneficial to have more or less momentum when competing in the SA race? Explain your reasoning

PHYSICS 2020 – 21 MINI-PROJECT CHALLENGE

Mousetrap Car ChallengeProject Description

Overview:

In this project, the crew is to design and construct a vehicle which uses a single mousetrap as its sole source of propulsion. The vehicle is to be designed for distance. In doing so, you must apply principles of friction, inertia, force, (angular) acceleration, momentum, rotational inertia, energy, torque and manipulate simple machines.

Objectives:

The student should have an understanding of the interrelationship of friction, inertia, force, acceleration, momentum, rotational inertia, energy, torque and simple machines. The student will show this understanding by designing and creating a mousetrap car for maximum distance, recording their research and explorations in a mousetrap car journal, and explaining how their car operates.

Event Description: Teams of 2-3 people will build a mousetrap-powered car designed to travel a maximum distance in a straight line; AND to travel the fastest for a specific distance.

Process

Step One: Research

Research mousetrap cars and how they work. Learn about the different factors that affect how far a mousetrap car can travel. Step Two: DesignOnce you have a good understanding of what makes a good mousetrap car, you will design a mousetrap car using the knowledge that you gained from the research. Your design will include side, top, and rear view “blueprints” of your vehicle. You will also include a list of materials needed to build the car. You must turn in this design and get it approved before you can move on to the next step.

Drawing #1: This is the first drawing of your vehicle. All features of the vehicle are to be illustrated and labeled. [DUE: Nov. 23, 2020]

Drawing #2: This is the final drawing of your vehicle. All features of the vehicle are to be illustrated and labeled, highlighting the additions and deletions from the first drawing.

All drawings are to be drawn to scale, completed on graph paper, drawn in pencil, and all lettering is to be in manuscript (printed) style. [DUE: Dec. 1, 2020]

Specifics in Designing the Mousetrap Vehicle:

1. Only one mousetrap may be used as the sole source of propulsion.

[The vehicle must be powered by a single Victor brand mouse trap measuring: 1 - 3/4 inches X 3 - 7/8 inches.]

2. The device cannot have any additional potential or kinetic energy at the start other than what can be stored in the mousetrap’s spring itself. (This also means you cannot push start your vehicle.)

The mouse trap cannot be physically altered except for the following:

holes can be drilled only to mount the mouse trap to a frame the mouse trap's snapper arm may be cut and lengthened

3. The spring of the mousetrap may not be altered in any way. This is a safety precaution. Winding the spring too tight can result in the spring breaking! The spring can be removed only to adjust the length of its lever arm.

Vehicles must be self-starting.

The vehicles must steer itself and may not receive a push in any direction in order avoid a collision.

4. The mousetrap must move forward with the vehicle. The mousetrap cannot be used to launch a toy car or other object to the required distance. It must be part of the vehicle.

5. The mousetrap must be permanently mounted to the chassis.

6. The vehicle must steer itself. Measurements of distance will not measure the total distance traveled, only the displacement distance (In other words, a straight line measurement).

7. The instructor has the final decision as to the appropriateness of any additional items that might be used in the construction of the vehicle.

8. Paint, decorate and name your vehicle!

Materials

All materials will be provided by the individual group members.

Step Three: BuildUsing your materials, build the car that you have designed. [DUE: Nov. 30, 2020]

Step Four: Test

Test your car and make adjustments to maximize the distance it can travel. You must keep a journal of each adjustment, the reason for the adjustment, and the effect of the adjustment (new distance covered). [DUE: Dec. 2, 2020]

Step Five: Distance AND Velocity Competition [DUE: Dec. 4, 2020]

1. The competition will take place in the field.

2. Each car must be ready for competition when called.

3. If you are not ready/prepared to race, you will forfeit your turn.

4. There will be two rounds of trials.

The greatest linear distance is not the total distance a vehicle travels but is defined as the displacement distance of the vehicle from the start line.

The greatest linear distance will be measured perpendicular from the front of the starting line to the point of the vehicle that was closest to the start line when released and will not "angle" to where the vehicle comes to rest.

Your score on the race portion of the project will be determined by the following formula:

The instructor has the final decision as to the appropriateness of any additional items that might be used in the construction of the vehicle.

Step Six: Report [DUE: Dec. 7, 2020]

Each group will turn in a report for the project with the following sections:

TitleObjectiveDiscussion/Theory This part of the report should address all of the following:

· How does a mousetrap car work? Explain by telling me how the energy moves through the mousetrap car from the spring. Include a definition of energy, potential energy, and kinetic energy.· Discuss concepts such as friction, inertia, force, acceleration, momentum, rotational inertia, energy, torque as they relate to the operation of a mousetrap car.· Identify the simple machines in your mousetrap car and the role they play in your vehicle.· Explain, in detail, how to make a mousetrap go as far as possible.

Your Final Design

Your Results from the Competition

Conclusion/Reflections Reflection: As a team, submit your answers to the following questions:

1. Analyze your mousetrap car's motion:a) How far did your car travel horizontally?b) How long did your car take to travel this far?c) What was your car's average velocity?

2. How did your group maximize the work done by the mousetrap spring on your car?3. What role did friction play in the performance of your car? Did it aid or hinder?4. Beginning with the stored mechanical energy in the spring, explain the multiple transformations the

energy goes through5. How did undertaking this project improve your understanding of work and energy?6. How did you feel about this project when it was first assigned?7. How do you feel about this project now that it has concluded?8. What would you have done differently as you and your team worked through this project?

ScoringDistance >0m >2m >5m >10m >12m Score

Points 2 4 6 8 10 Velocity Calculations complete done w/AFSA correct Score

Points 1 3 5 Completion on time Score

Points 25 Energy Transformations 1 2 3 4 >=5 Score

Points 2 4 6 8 10

Reflection turned in sheet answered completely introspective and thoughtful Score

Points 1 3 5