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Agenda Warm Up N’s 3 Laws Forces in Equilibrium Tension in a String

Warm Up

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Agenda Warm Up N’s 3 Laws Forces in Equilibrium Tension in a String

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  1. Warm Up In a rescue attempt, a hovering helicopter drops a life preserver to a swimmer being swept downstream by a river current of constant velocity v. The helicopter is at a height of 9.8 m. The swimmer is 6.0 m upstream from a point directly under the helicopter when the life preserver is released. It lands 2.0 m in front of the swimmer. How fast in the current flowing? Neglect Air resistance. a) 13.7 m/s b) 9.8 m/s c) 6.3 m/s d) 2.8 m/s e) 2.4 m/s AP PhysicsMonday 13.10.21Standards: 2c2 Students should understand the motion of projectiles in a uniform gravitational field. Objective: SWBAT solve 2D Relative Motion Problems Agenda • Warm Up • N’s 3 Laws • Forces in Equilibrium • Tension in a String Homework Relative Motion 2-5 p.29

  2. Warm Up What are the 3 equations of motion? Write them down without looking at notes or asking your neighbors? AP PhysicsTuesday 13.10.22 Standards: 2c2 Students should understand the motion of projectiles in a uniform gravitational field. Objective: SWBAT solve problems involving relative velocity. Agenda • Warm Up • Diagram an AP Free Response Question Homework Study for Exam

  3. AP PhysicsWednesday 13.10.23Standards: 2c1 Students should understand the motion of projectiles in a uniform gravitational field. Objective: SWBAT score 5’s on this test. Warm Up How did you study for the Test Last night? 3 min. Agenda • Warm Up • Take Kinematics Test Homework NA

  4. Warm Up What do you know about forces. Fill up the box. If you know little, ask some questions about forces. AP PhysicsThursday 13.10.24Standards: B1 Static Equilibrium 1st Law, B2 students understand the relationship between force & acceleration. Objective: SWBAT find solutions to balancing forces problems. Agenda • Warm Up • N’s 1st Law Reading • 1st law worksheet Homework Balancing Tension Force Worksheet 3a

  5. Warm Up Find the missing Tension Forces for this system at equilibrium. AP PhysicsFriday 13.10.25Standards: 2b1 Draw a well labeled, free-body diagram. Objective: SWBAT create free body diagrams from written and drawn scenarios. 45° T1 Agenda • Warm Up • Net Force & Free Body Diagrams • Practice In Class p.32, 1-3 T2 50 kg Homework Newton’s 2nd Law Practice

  6. How to complete the lab write Up • Come up with a question or hypothesis that you think you can prove. : ex. hyp. The 3 equations of motion will predict the motion of a following marble enabling us to break an egg. • Write down materials & procedures used and write down your procedure for setting up the experiment and implementing the experiment. (Do not include anything about calculations in this section) • Data: Use the scant information that you have to make a parabolic graph that represents the position of the marble. We do not have time data so we will just graph vertical and horizontal position y vs. x • Questions you will need to answer in your Calculations portion of the lab: • 1. What was the projectile’s initial velocity? • 2. How long was the projectile in the air before it hit the egg? • 3. Find the components of velocity of the marble as it goes through each of the three rings and as it hits the egg • 4. What was the projectile’s final speed and angle as it hits the egg? • Analysis: In this section just justify your results using data. This entails evaluating your hypothesis as true, false, or inconclusive and provide it with actual data. One thing you might try proving is that the motion is parabolic. It may help depending on whether you are arguing for true, false, or inconclusive. • Conclusion: Summarize your results: Include important data that you got from the lab. Talk about and name some sources of error. Talk about and name any design changes or improvements you’d make to the lab.

  7. New AP Lab Write Up Format

  8. Group Poster/Formal Problem Write Up Rubric

  9. Newton’s First Law The Law of Inertia – “In the absence of an unbalanced applied force (Fnet=0), a body at rest remains at rest, and a body already in motion remains in motion with a constant velocity (constant speed and direction) If there is no net force an object initially at rest will stay at rest. If there is no net force and object initially moving will stay moving. This means that objects resist changes in their motion. It is hard to make objects speed up or slow down. You have to force them to do it, by applying a force.

  10. AP Kinematics Test Review: Poster or Formal Problem Write Up A cannonball is shot with an initial speed of 35 m/s at a launch angle of 35° toward a castle wall 110 m away. The height of the wall is 40m. Assume that effects due to the air are negligible. (for this problem use g=9.8m/s2). • Show that the cannonball will strike the castle wall. (This means using no numbers. You can do this last if you like) • How long will it take for either the cannonball to strike the wall? t=3.82s • At what height above the base of the wall will the cannonball strike? hw(cb)=5.2m

  11. Conventions for Physics Diagrams for drawing for drawing distance 5kg speed vs d horizontal displacement velocity v Δx vertical displacement. for drawing a Δy acceleration mass Δx time t

  12. Types of Forces among others

  13. Newton’s 2nd Law of Motion When you are dealing with Force Problems you need to add up all of the x components of Force and all of the y components of Force separately. we write it like this: Fx= Fx1+Fx2+Fx3+Fx4+…FxN=Fnetx all these fancy symbols mean you add up all of the forces in the x direction to get the total force acting on the object. Fy= Fy1+Fy2+Fy3+Fy4+…FyN=Fnety same for the y direction. Get used to breaking Force vectors into components to solve problems. You can’t deal with vectors at an angle without breaking them into components.

  14. Free Body Diagrams How to draw a free body diagram. 1. Represent the object of interest with a dot. • Make an arrow for every Force acting on that object in the direction that the Force is pointing. • Only include Forces in this type of diagram. This is separate from previous diagrams we have used to solve problems. • The Arrows should never point towards the object. • Label the Forces. Fap 30° W

  15. Free Body Diagram Practice Problem In the early morning, a park ranger in a canoe is observing wildlife on the nearby shore. The Earth’s gravitational force on the ranger is 760N downward and its gravitational force on the boat is 190N downward. The water keeps the canoe afloat by exerting a 950N force upward on it. Draw a free body diagram of the canoe. Extra Practice: p.42 Cracking the AP Physics B Exam

  16. Free Body Diagram Practice3b For each of the following problems create a free body diagram. Where asked, answer questions. • A piano falls from the sky and air makes it reach terminal velocity • A cart from an amusement park ride is accelerated up at an angle θ. Assume friction is negligible, but air resistance is significant. • The cart from problem 2 drops at a very steep angle of ϕ. • A 70kg rock falls from the cliff and the air provides an upwards force of 30N. • A 65kg skydiver opens her parachute. Air resistance to her body is 20 N and the Lift Force is 617N. What is the Net Force acting on her? • A 25kg child rolls down a hill angled 60° to the horizontal. Friction is significant. • A 15kg chandelier is attached to the ceiling using a cable. • A 25kg child is hanging stationary from monkey bars. One arm is angled at 30° and the other arm is angled at 60°. • **A cart is sitting on a table and attached to a pulley by a string. The other side of the pulley has a mass M attached to the bottom. Both objects are stationary. Find the free body diagram of the cart and of the mass separately.

  17. Newton’s 2nd Law Practice 3c • A car is accelerated east with a 2000 N Force. Friction resists the car’s motion with 120N and air resistance contributes another 35 N. What is the net Force acting on the car? • A bike rider pushes his/her bike pedals with a Force of 200N. This only accelerates the bike at 1m/s2. If s/he and the bike have a combined mass of 150kg, how much resistive Force was acting on the bike? • How much is A different car with a mass of 750 kg accelerates at a rate of 2m/s2. If Friction resists the motion with 180 N of force and air resistance with another 35 N, how much Force was applied by the engine? • A toy 0.5 kg toy car is accelerated from rest with a 20 N force for 3 seconds. How far did the car travel? • A child is on a table flicking marbles to see how far they will fly. A 0.25 kg marble is flicked from rest by the child. The child applies 4 N of Force with her finger that lasts 0.5 seconds. Afterwards, if the marble travels at a constant velocity until it flies off of the 2 m high table (assume no friction), how far away from the table did the marble land? • A rope of negligible mass supports a block that weighs 30 N, as shown above. The breaking strength of the rope is 50 N. The largest acceleration that can be given to the block by pulling up on it with the rope without breaking the rope is most nearly what? • A horizontal, uniform board of weight 125 N and length 4 m is supported by vertical chains at each end. A person weighing 500 N is sitting on the board. The tension in the right chain is 250 N. What is the tension in the left chain? • The cart of mass 10 kg shown above moves without frictional loss on a level table. A 10 N force pulls on the cart horizontally to the right. At the same time, a 30 N force at an angle of 60° above the horizontal pulls on the cart to the left. What is the magnitude of the horizontal acceleration of the cart? • A 100 N weight is suspended by 2 chords as shown above. The Tension on the slanted chord is? • When an object of weight W is suspended from the center of a massless string as shown above, the tension at any point in the string is? #7 #8 #9 #10

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