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Interpreting Free Body Diagrams

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Interpreting Free Body Diagrams

  1. 1. Mary pulls on a lawnmower parallel to the ground. The mower moves at a constant speed up the hill. 1 3 4 Which free body diagram best represents the forces on the mower? x y x y x y x y 2
  2. 2. Mary pulls on a lawnmower parallel to the ground. The mower moves at a constant speed up the hill. 1 3 4 Which free body diagram best represents the forces on the mower? x y x y x y x y 2
  3. 3. Stacey pulls a mower at 40-degrees relative to the ground. 1 2 3 4 Which free body diagram best represents the forces on the mower? x 40 0 y y x 40 0 x y 40 0 y x 40 0
  4. 4. Stacey pulls a mower at 40-degrees relative to the ground. 1 2 3 4 Which free body diagram best represents the forces on the mower? x 40 0 y y x 40 0 x y 40 0 y x 40 0
  5. 5. Marsha pulls a sled on ice (no friction). The rope exerts a 150-N force at an angle of 20 0 above horizontal. The mass of the sled and her brother is 45 kg. g = 10 m/s 2 . Stacey represented this situation pictorially and mathematically. Did the student mislabel or forget to include anything? 1 (150 N) should be (150 N) sin 20 o . 2 (150 N) should be (150 N) cos 20 o . 3 Include a +(150 N) sin 20 o term in the y equation. x x : (150 N) = (45 kg) a x y : N – (45 kg)(10 m/s 2 ) = (45 kg) 0 4 Both (1) and (3) need corrections. 5 Both (2) and (3) need corrections.
  6. 6. Marsha pulls a sled on ice (no friction). The rope exerts a 150-N force at an angle of 20 0 above horizontal. The mass of the sled and her brother is 45 kg. g = 10 m/s 2 . Stacey represented this situation pictorially and mathematically. Did the student mislabel or forget to include anything? 1 (150 N) should be (150 N) sin 20 o . 2 (150 N) should be (150 N) cos 20 o . 3 Include a +(150 N) sin 20 o term in the y equation. x x : (150 N) = (45 kg) a x y : N – (45 kg)(10 m/s 2 ) = (45 kg) 0 4 Both (1) and (3) need corrections. 5 Both (2) and (3) need corrections.
  7. 7. What are the missing signs? x : (150 N) cos 20 o = (45 kg) a x y : __ N __ (45 kg)(10 m/s 2 ) __ (150 N) sin 20 o = 0 1 + – + 2 + + – 3 – – + 4 – – – 5 + + + Steve pulls a sled on ice (no friction) with a 150-N force at an angle of 20 0 . The mass of the sled and her brother is 45 kg. g = 10 m/s 2 . Stacey represented this pictorially and mathematically. x o
  8. 8. What are the missing signs? x : (150 N) cos 20 o = (45 kg) a x y : __ N __ (45 kg)(10 m/s 2 ) __ (150 N) sin 20 o = 0 1 + – + 2 + + – 3 – – + 4 – – – 5 + + + Steve pulls a sled on ice (no friction) with a 150-N force at an angle of 20 0 . The mass of the sled and her brother is 45 kg. g = 10 m/s 2 . Stacey represented this pictorially and mathematically. x o
  9. 9. Which diagram best represents the forces exerted on the car by the Earth and the Earth’s surface? The motion of a car is represented with the motion diagram below. x y 4 o x x y 1 x y 2 x y 3 x y 5
  10. 10. Which diagram best represents the forces exerted on the car by the Earth and the Earth’s surface? The motion of a car is represented with the motion diagram below. x y 4 o x x y 1 x y 2 x y 3 x y 5
  11. 11. Which word description below best matches the above mathematical description? <ul><li>The 0.80 N force of the Earth on the object causes its speed in the x direction to increase from 0 to 16 m/s. </li></ul><ul><li>The object slows down due to a 0.80 N frictional force. </li></ul><ul><li>The object has a 10 m/s 2 acceleration in the y direction. </li></ul><ul><li>The net force causing the object to slow down is exerted in the same direction as the initial velocity. </li></ul><ul><li>5 The object’s velocity increases from 0 to 16 m/s. </li></ul>x : 0 – (0.80 N) = (1000 kg) a x y : N – (1000 kg)(10 m/s 2 ) = (1000 kg) 0 0 – 16 m/s = a x t
  12. 12. Which word description below best matches the above mathematical description? <ul><li>The 0.80 N force of the Earth on the object causes its speed in the x direction to increase from 0 to 16 m/s. </li></ul><ul><li>The object slows down due to a 0.80 N frictional force. </li></ul><ul><li>The object has a 10 m/s 2 acceleration in the y direction. </li></ul><ul><li>The net force causing the object to slow down is exerted in the same direction as the initial velocity. </li></ul><ul><li>5 The object’s velocity increases from 0 to 16 m/s. </li></ul>x : 0 – (0.80 N) = (1000 kg) a x y : N – (1000 kg)(10 m/s 2 ) = (1000 kg) 0 0 – 16 m/s = a x t
  13. 13. Which FBD best represents the above motion diagram for a car? x y 2 x y 1 x y 3 x y 4
  14. 14. Which FBD best represents the above motion diagram for a car? x y 2 x y 1 x y 3 x y 4
  15. 15. 1 5 Either 2 or 4 are possible 4 2 3 Which motion diagram best represents the situation shown in the free-body diagram?
  16. 16. 1 5 Either 2 or 4 are possible 4 2 3 Which motion diagram best represents the situation shown in the free-body diagram?
  17. 17. 1 Which FBD below best represents the forces exerted on the ball as it moves DOWN (ignore air resistance)? 2 3 4
  18. 18. 1 Which FBD below best represents the forces exerted on the ball as it moves DOWN (ignore air resistance)? 2 3 4
  19. 19. 1 Which FBD below best represents the forces exerted on the ball at the TOP of its path? 2 3 4 5 No forces are exerted on the ball
  20. 20. 1 Which FBD below best represents the forces exerted on the ball at the TOP of its path? 2 3 4 5 No forces are exerted on the ball
  21. 21. x y Which speed versus time chart best represents this situation? 1 2 3 v t v t v t
  22. 22. x y Which speed versus time chart best represents this situation? 1 2 3 v t v t v t

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