Newton’s Laws Notes - Birmingham Schools · Web viewDraw a freebody diagram for this situation....

2016 AP Physics 1 Notes Chapter 4

Newton’s Laws: Let the Force be with you!

1. What is inertia?

2. What is a force?

Definition Vector/Scalar Units Conversion What is a freebody diagram?

3. What is Newton’s 1st law?

a. Where did we see Newton’s 1st law with projectiles?

b. Draw a free body diagram for an elevator moving upwards at a constant speed.

4. Consider an elevator going upwards at a constant speed. The force of the rope on the elevator is __________ the force of gravity on the elevator.

a. Greater thanb. Less thanc. The same as

5. 1st Law Demonstrations:

6. What is Newton’s 2nd Law?

What is inertia?

Know Newton’s 1st law and how it apply it to demonstrations

TableclothHoop/nut/bottle


a. If you squeeze a dry sponge what changes? Mass, Volume, Inertia, Density

b. If an object is accelerating what are its possible motions?

c. What is the force due to gravity? Where would it be better to buy gold sold by weight? Denver or Death Valley?

d. A diver dives into water, the water slows him to a stop. How do the force of water and gravity compare?

7. If you drop a feather and a hammer on the moon, which will strike the surface first? Use Newton’s 2nd law to explain why.

8. What is the normal force?

a. If you press down on a book what happens to the normal force?

b. What is the direction of the normal force if a book is pressed to a wall?

Know the difference between mass and weight

Know what normal force is, how to draw it in a freebody diagram and be able to calculate it.

Why would normal equal weight?


9. What are the possible forces for a freebody diagram?Force Name What clue tells me it’s

present?What direction does this force point in?

10. A 5 kg bucket of water is raised from a well by a rope. If the upward acceleration of the bucket is 3 m/s2, find the force exerted by the rope on the bucket.

a. Draw a freebody diagram for this situation.

b. Write Newton’s 2nd law equations based on your freebody diagram (vector addition).

c. Calculate the force exerted by the rope on the bucket.

11. To lift Arlo, four nurses grip the sheet on which he is laying and lift upward. If each nurse exerts an upward force of 240 N and Arlo has an upward acceleration of 0.504 m/s2, what is Arlo’s weight?

a. Draw a free body diagram based on this situation

b. Write Newton’s 2nd law equations based on your freebody diagram

c. Calculate Arlo’s weight


12. Arlo is on an elevator. His weight is 500N and the graph to the right shows the scale reading as a function of time as the elevator moves upward. At time zero velocity is zero.

a. Draw a free body diagram for Arlo.

b. What force does not change due to motion?

c. What force does a scale read?

d. Calculate Arlo’s mass.

Time interval 0 to 5 seconds 5 to 10 seconds 10 to 15 seconds 15 to 20 secondsMotion of elevator

Newton’s 2nd Law EquationFilled in Newton’s 2nd Law equationCalculated Acceleration

e. What force determines how Arlo feels?

“feeling” Direction of acceleration Comparison of forcesLight

Normal

Heavy

f. Draw the corresponding velocity vs time graph.

Draw a freebody diagram, write Newton’s 2nd Law equations, Solve equations for Normal force for a person on an elevator that is*Accelerating*Traveling with a constant velocity*At rest


13. Alice (60kg) is standing on a spring scale in an elevator. Starting from rest, the elevator ascends, attaining its maximum speed of 1.6 m/s in 0.8 s. It travels this constant speed for 4 seconds, undergoes a uniform negative acceleration for 2 seconds, and comes to rest.

a. Draw Alice’s freebody diagram.

b. What does the spring scale read while the elevator speeds ups?

c. What does the spring scale read while the elevator moves at a constant speed?

d. What does the spring scale read while the elevator slows down?

14. A 20N thrust is exerted on a 0.50 kg rocket for a time interval of 8.0 s. The rocket then coasts upward more distance until its speed is reduced to zero. Upon reaching its maximum height, the rocket deploys a parachute, and then descends vertically to the ground. Determine the maximum height of the rocket.

a. On the figures below, draw and label a free-body diagram for the rocket during each of the following intervals.

Draw a velocity vs time graph of a motion


a. Write Newton’s 2nd law equations for while the engine is firing and solve for acceleration.

b. Calculate the velocity of the rocket after 8.0 seconds.

c. Calculate the height of the rocket after 8.0 seconds.

d. Calculate the maximum height of the rocket

15. Arlo pushes a crate with 100 N and there is a frictional force of 20N against the crate. The crate has a mass of 50 kg, find the acceleration of the crate.

a. Draw a freebody diagram

b. Write Newton 2nd Law equations (2 now!)

Be able to apply what you know about forces to draw a freebody diagram for any situation.

Given your freebody diagram write relevant Newton’s 2nd Law equations.

Solve your Newton’s

You are expected to be able to solve multiple step acceleration/freefall problems.


c. Calculate the acceleration of the crate.

16. A 150 N bird feeder is supported by three cables as shown. Find the tension in each cable.

a. Draw a freebody diagram of the bird house

b. Write Newton’s 2nd Law equations (2 now!).

c. How much tension does the bird house produce in the cables?

17. The distance between two telephone poles is 50.0m. When a 1.00 kg bird lands on the telephone wire midway between the poles, the wire sags 0.200 m.

a. Draw a freebody diagram of the bird

b. Write Newton’s 2nd Law equations.

c. How much tension does the bird produce in the wire?



Solve your Newton’s



Possible forces:*Tension*Weight*Normal*Friction*Push/PullKnow when each is present and which way


18. A icy hill is inclined at an angle of 30 degrees. Determine the acceleration of a car on that hill if it starts at rest.

a. Draw a free body diagram

b. Write Newton’s 2nd law equations

c. Calculate the acceleration of the car.

19. Newton’s Third Law

a. Horse and Cart

b. If the Earth exerts 1000N on an orbiting communications satellite what is the force on the Earth by the satellite? Why doesn’t the Earth orbit the satellite?

Know Newton’s 3rd Law and apply it to a horse pulling a cart and water rockets

Draw a freebody diagram, write Newton’s 2nd Law equations, Solve equations for a car on an inline plane.


20. If a Mack truck and a Volkswagen have a head on collision, which vehicle will experience the greater impact force?a. The mack truckb. The Volkswagenc. Both the samed. It depends on other factors.

21. Each of the figures to the right shows a tractor attached to an object. The tractor exerts the same force on each object. Which of the following is a true statement about an object and the relative magnitude of the force exerted by the object on the tractor?

a. The magnitude of the force exerted by the truck on the tractor is greatest, because the resulting motion is the direction opposite the tractor’s pull

b. The magnitude of the force exerted by each object on the tractor is equal, because the tractor exerts an equal force on each object

c. The magnitude of the force exerted by the boulder on the tractor is the least, because no motion results.

d. The magnitude of the force exerted by the wagon on the tractor is least, because the resulting motion is in the direction of the tractor’s pull.

22. Alice is standing on ice and is holding a rope connected to a sled. If Alice pulls with a force of 2N, what force does the sled exert on Alice?

a. Do Alice and the sled have the same acceleration? If Alice’s mass is 45 kg, what is her acceleration? If the sled is 10 kg what is its acceleration?

Apply Newton’s 3rd Law to situations where objects are connected by rope


23. Consider a car at rest. We can conclude that the downward gravitational pull of Earth on the car and the upward contact force of Earth on it are equal and opposite because

a. The two forces form an interaction pair (3rd law)b. The net force on the car is zero (2nd law)c. Neither of the above

24. How do the tensions in the ropes compare?

a. In the space below, draw a free-body diagram of each box, showing and labeling all the forces present.

b. If the blocks are 10 kg each and are pulled by a force of 100 N what is the acceleration of the system?

c. Find the tension between each of the blocks.



Solve your Newton’s 2nd Law equations for unknown.

Possible forces:*Tension*Weight*Normal*Friction*Push/PullKnow when each is present and which way they point


25. Two small blocks, each of mass 3 kg. Block A is placed on a smooth tabletop as shown above, and block B hangs over the edge of the table.

The tabletop is a distance 2.8 m above the floor. Block B is then released from rest at a distance 1.4 m above the floor at time t = 0.

(a) In the space below, draw a freebody diagram of each box, showing and labeling all the forces present.

(b) Determine the acceleration of block B as it descends.

(c) Describe the motion of block A from time t = 0 to the time when block B strikes the floor.

(d) Describe the motion of block A from the time block B strikes the floor to the time block A leaves the table. (2pts)





Know Newton’s 1st law and how to apply it

Solve problems using constant acceleration


26. Three objects are connected by light strings. The string connecting the 4.00 kg object and the 5.00 kg object passes over a light frictionless pulley.

a. Draw a freebody diagram for each of the three objects.

b. Write the Newton 2nd law equations for all three objects.

c. Find the acceleration of each object.

d. Find the tension in rope connecting the 5 kg and 4 kg masses.

e. Find the tension in the rope connecting the 4 kg and 3 kg masses.





5 kg mass 4 kg mass 3 kg mass


27. The three blocks of masses 10.0 kg, 5.00 kg, and 3.00 kg are connected by light strings that pass over frictionless pulleys as shown. The acceleration of all of the blocks is 2.00 m/s2 to the left, and the surfaces are frictionless.

a. Draw a free body diagram for each block

10 kg 5 kg 3 kg

b. Write Newton’s 2nd Law equations for each block10 kg 5 kg 3 kg


Draw a freebody diagram, write Newton’s 2nd Law equations, Solve equations for an object on an inline plane.




Apply Newton’s 3rd Law to situations where objects are connected

10 kg

5.00 kg3.00 kg

200


28. The hanging block is 3kg, the block on the ramp is 5kg. The angle of the ramp is 30 degrees.a. Draw the free body diagram for each block.

b. What is the acceleration of the blocks?

c. What is the tension in the cord?

29. Two types of frictiona. Static friction




Apply Newton’s 3rd Law to situations where objects are connected

Draw a freebody diagram, write Newton’s 2nd Law equations, Solve equations for an object on an inline plane.

Know the difference between static and kinetic friction.


b. Kinetic Friction

30. While Arlo loads crates onto a ship he finds that a 20 kg crate initially at rest on a horizontal surface, requires a 75N horizontal force to set it into motion, However, after the crate is in motion, a horizontal force of 60N is required to keep it moving with a constant speed. Find the coefficients of static and kinetic friction.

31. For each of the following, draw a freebody diagram and write Newton 2nd Law equations.

a. You press your physics textbook flat against a vertical wall with your hand.

b. A 10 kg block is at rest on an inclined plane.

c. A block is sliding down an inclined plane

d. Alice pushing a filing cabinet but it doesn’t move.

e. A hockey puck sliding on ice and slowing down

f. Arlo pulling a crate with a force at a 30 degree angle with the horizontal and at a constant speed

32. Bock B weighs 711 N. The coefficient of static friction between block and table is 0.25; assume that the cord between B and the knot is horizontal.




B 30 knot


a. Draw a free body for block B, block A and the knot. (system is at rest)Block B Block A Knot

b. Write all Newton 2nd law equations (system is at rest)Block B BlockA Knot

c. Find the maximum weight of block A for which the system will be stationary.

33. Alice decides to move a box of books into her dormitory room by pulling on a rope attached to the box. She pulls with a force of 80 N at an angle of 25 degrees above the




A


horizontal. The box has a mass of 25 kg and the coefficient of kinetic friction between box and floor is 0.3. a. Draw a freebody diagram for the box.

b. Write Newton’s 2nd Law equations

c. Calculate the acceleration of the box.

Homework – NewtonName__________________

1. If you were in a spaceship and launched a cannonball into frictionless space, how much force would have to be exerted on the ball to keep it going?


2. If you hold a coin above your head while in a bus that is not moving, the coin will land at your feet when you drop it. Where will it land if the bus is moving in a straight line at constant speed? Explain.

3. Many automobile passengers suffer neck injuries when struck by cars from behind. How does Newton’s law of inertia apply here? How do headrests help to guard against this type of injury?

4. If an elephant were chasing you, its enormous mass would be very threatening. But if you zigzagged, the elephant’s mass would be to your advantage. Why?

5. In the cabin of a jetliner that cruises at 600 km/h, a pillow drops from an overhead rack into your lap below. Since the jetliner is moving so fast, why doesn’t the pillow slam into the rear of the compartment when it drops? What is the horizontal speed of the pillow relative to the ground? Relative to you inside the jetliner?

Newton’s Laws Notes - Birmingham Schools · Web viewDraw a freebody diagram for this situation....

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