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2011 2nd Trimester Honors Notes Newton’s Laws Notes Name ________________ 1. What is inertia? 2. What is a force? a. What is it measured in? b. What is a freebody diagram? Draw one for a sign hanging. 3. Newton’s 1st law a. 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 than b. Less than c. The same as 5. 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 Net Force vector equations. 2011 2nd Trimester Honors Notes c. How much tension does the bird produce in the wire? 6. 1st Law Demonstrations: 7. Newton’s Second Law 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? d. A diver dives into water, the water slows him to a stop. How do the force of water and gravity compare? 8. 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. 2011 2nd Trimester Honors Notes 9. A performer in a circus is fired from a cannon as a “human cannonball” and leaves the cannon with a speed of 18.0 m/s. The performer’s mass is 80.0 kg. The cannon barrel is 9.20m long. Find the average net force exerted on the performer while he is being accelerated inside the cannon. 10. An airplane accelerates uniformly from rest. A physicist passenger holds up a thin string of negligible mass to which she has tied her ring, which has a mass m. She notices that as the plane accelerates down the runway, the string makes an angle with the vertical as shown above. a. In the space below, draw a free-body diagram of the ring, showing and labeling all the forces present. The plane reaches a takeoff speed of 65 m/s after accelerating for a total of 30 s. b. Determine the minimum length of the runway needed. c. Determine the angle B that the string makes with the vertical during the acceleration of the plane before it leaves the ground. 2011 2nd Trimester Honors Notes 11. How do the tensions in the ropes compare? a. If the blocks are 10 kg each and are pulled by a force of 100 N what is the acceleration of the system? b. Find the tension between each of the blocks. 12. 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. 5 kg mass 4 kg mass 3 kg mass nd b. Write the Newton 2 law equations for all three objects. 2011 2nd Trimester Honors Notes 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. 13. 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. Determine the maximum height of the rocket. a. Draw a freebody diagram during launch b. Write Newton’s 2nd law equations c. Find the velocity of the rocket after 8.0 seconds. 2011 2nd Trimester Honors Notes d. Find the height of the rocket after 8.0 seconds. e. Find the maximum height of the rocket 14. 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? 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 c. Solve Newton 2nd Law equations 2011 2nd Trimester Honors Notes 16. 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. What is the acceleration of the car? 17. Arlo is on an elevator. His mass is 72.2 kg. a. Draw a free body diagram. b. What is the scale reading when the elevator is at rest? c. If the elevator (starting from rest) reaches 3m/s in a time of 2 seconds what is it’s acceleration? d. What does the scale read during part “c”? (If the elevator is moving upwards) 2011 2nd Trimester Honors Notes e. If the elevator stays at 3 m/s for 5 seconds what does the scale read? f. If the elevator slows to rest in 4 seconds, what does the scale read? g. When did Arlo feel the “lightest”, the “heaviest”? 18. 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? 2011 2nd Trimester Honors Notes 19. 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 rough. 5.00 kg 3.00 kg 10 kg 200 a. Draw a free body diagram for each block 10 kg 5 kg 3 kg b. Write Newton’s 2nd Law equations for each block 10 kg 5 kg 3 kg 20. 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? 2011 2nd Trimester Honors Notes 21. If a Mack truck and a Volkswagen have a head on collision, which vehicle will experience the greater impact force? a. The mack truck b. The Volkswagen c. Both the same d. It depends on other factors. 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? 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. Two types of friction a. Static friction b. Kinetic Friction 25. Demonstration 2011 2nd Trimester Honors Notes 26. For each of the following, draw a freebody diagram and write Newton 2nd Law equations. a. You press your physics d. Alice pushing a filing textbook flat against a cabinet but it doesn’t vertical wall with your move. hand. b. A 10 kg block is at rest e. A hock puck sliding on on an inclined plane. ice and slowing down c. A block is sliding down f. Arlo pulling a crate with an inclined plane a force at a 30 degree angle with the horizontal and at a constant speed 2011 2nd Trimester Honors Notes 27. 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. knot 30 B A a. Draw a free body for block B, block A and the knot. Block B Block A Knot b. Write all Newton 2nd law equations Block B BlockA Knot c. Find the maximum weight of block A for which the system will be stationary. 2011 2nd Trimester Honors Notes 28. A 1000N crate is being pushed across a level floor at a constant speed by a force F of 300N at an angle of 20 degrees below the horizontal. b. Draw a freebody diagram c. Write Newton 2nd Law equations d. What is the coefficient of kinetic friction between the crate and the floor? e. If the 300 N force is instead pulling the block at angle of 20 degrees above the horizontal what will be the acceleration of the crate? 2011 2nd Trimester Honors Notes 29. 100N 50N a. Draw a freebody diagram for each block b. What is the minimum force of friction required to hold the system in equilibrium? c. What coefficient of static friction between the 100 N block and the table ensures equilibrium? d. If the coefficient of kinetic friction between the 100N block and the table is 0.250, what hanging weight should replace the 50.0N weight to allow the system to move at a constant speed once it is set in motion? 2011 2nd Trimester Honors Notes 30. A 5.0 kg penguin sits on a 10 kg sled. A horizontal force of 45 N is applied to the sled, but the penguin attempts to impede the motion by holding onto a cord attached to a tree. The coefficient of kinetic friction between the sled and snow as well as that between the sled and the penguin is 0.20. a. Draw a free-body diagram for the penguin and one for the sled. Penguin Sled b. Identify the reaction force for each force in your diagrams. c. Find the tension in the cord d. Find the acceleration of the sled. 2011 2nd Trimester Honors Notes Homework – Newton Name__________________ 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?