Physics Test 6: Dynamics
Physics Test 6: Dynamics page 1
Multiple Choice
Read each question and choose the best answer by putting the corresponding letter in the blank to the left.
___C_______ 1. What was the ancient Greek philosophers’ strongest argument for giving greater
§§6.1–2 credence to reason rather than to experimentation?
A. Moving objects naturally tended to slow down over time.
B. Hot air naturally sought to rise into the heavens.
C. The material world was corrupt while reason was naturally perfect.
D. Heavy objects naturally sought to fall to the center of the earth.
B
__________ 2. Who inductively suggested the idea of inertia?
§6.4
A. Aristotle
B. Galileo
C. Tycho Brahe
D. Newton
___C_______ 3. The SI unit of force is the §6.5
A. kilogram.
B. gram.
C. newton.
D. slug.
___C_______ 4. Which is an example of a system on which unbalanced forces act?
§6.6
A. a picture hanging on a wall
B. a car moving at a constant speed down a straight street
C. a child sliding down a waterslide
D. a passenger aircraft flying at an assigned altitude
B
__________ 5. The force that acts with one or more other forces to produce mechanical equilibrium is called the §6.7
A. resultant.
B. equilibrant.
C. concurrent force.
D. weight.
___B_______ 6. A radiometer is an instrument that consists of a glass bulb containing tiny metal plates
§6.8 attached to an axle. These metal plates rotate when light strikes them. What type of force makes the plates rotate?
A. gravitational force
B. electromagnetic force
C. strong nuclear force
D. weak nuclear force Physics Test 6: Dynamics page 2
__________ 7. Which of the following is not a mechanical force?
D
§6.9
A. tension
B. compression
C. shear
D. gravity
D
__________ 8. The force of water against a sandbag wall is what kind of contact force?
§6.9
A. tension
B. shear
C. compression
D. friction
A
__________ 9. When you pull a glazed sheet of paper from underneath a neatly stacked pile of coins, the coins remain stacked afterward. Which of Newton’s three laws does this exhibit?
§6.12
A. first law
B. second law
C. third law
D. universal law of gravitation
___A______ 10. A force of 15.0 N gives an object an acceleration of 7.50 m/s2. What force would be needed to give it an acceleration of 2.0 m/s2?
§6.13
A. 4.0 N
B. 112.5 N
C. 2.0 N
D. 7.5 N
C
_________ 11. When you push on a heavy, immovable boulder, the boulder also pushes on you. This is an example of which of Newton’s laws?
§6.14
A. first law
B. second law
C. third law
D. universal law of gravitation
C
_________ 12. The kick from the firing of a high-powered rifle illustrates which of Newton’s laws?
§6.14
A. first law
B. second law
C. third law
D. universal law of gravitation
___D______ 13. Acceleration can be calculated by
§6.14
A. dividing an individual force by weight.
B. dividing an individual force by mass.
C. dividing a resultant force by weight.
D. dividing a resultant force by mass. Physics Test 6: Dynamics page 3
_________ 14. What is the mass of a 5000 N car?
D
§6.16
A. 50 kg
B. 51 kg
C. 500 kg
D. 510 kg
True/False
Read the following statements. Identify each as true or false by putting T or F in the blank to the left.
T
_________ 15. Scientific laws hold in every case in which they are tested.
§6.1
T
_________ 16. In the absence of air resistance, all objects fall at the same rate.
§6.2
F
_________ 17. Newton was the first person to assert the concept of inertia.
§6.3
T
_________ 18. Forces always cause a change in motion.
§6.7
___T______ 19. A spring scale is an example of an instrument used to measure forces.
§6.10
T
_________ 20. Newton’s first law of motion predicts that without unbalanced forces, moving objects will travel in straight lines.
§6.12
F
_________ 21. Under ideal conditions, an object needs a continuous push to maintain a constant velocity.
§6.12
___F______ 22. The action and reaction pairs act on the same system.
§6.14
___T______ 23. Forces can occur only in pairs.
§6.14
F
_________ 24. The weight of an object on Pluto is the same as its weight on Earth.
§6.16
___F______ 25. A triple-beam balance measures the weight of an object.
§6.16
Short Answer
After reading each sentence, write a response in the blank provided.
§6.4 26. For what phenomena do Newton’s laws of motion not always hold true?
Newton’s laws do not always hold true for particles that are extremely small or objects that move very fast. forces
§6.5 27. Pushes and pulls are simple descriptions for the phenomena physicists call _________________. weight
§6.7 28. The force of gravity acting on a mass is its ______________.
§6.8 29. The force-like interactions between subatomic particles within an atom’s nucleus are called nuclear forces or interactions
____________________________. tension (or tensile forces)
§6.9 30. The primary mechanical force transmitted through a tug-of-war rope is ______________________.
§6.9 31. The system of mathematics used to describe and explain noncontact forces is called field theory
_______________________. dynamics
§6.11 32. Newton’s laws of motion are the basis for the area of physics known as __________________.
Physics Test 6: Dynamics page 4 mechanical
§6.12 33. When the vector sum of all forces on a system is zero, the system is said to be in equilibrium
__________________. halved
§6.13 34. If the external force acting on a body of constant mass is halved, its acceleration is .
§6.15 35. (DS) Naval architects use an arresting wire system on an aircraft carrier to stop landing aircraft increases because this system ____________________ the amount of time the stopping force is applied, and reduces thus ________________ its magnitude on the pilot and aircraft. pound-force (lbf)
§6.16 36. The English Engineering System (EES) unit for weight is the ______________________.
Application Problems
Complete the problems below. Be sure to show your work, consider significant figures, and put your answer with the correct units in the blank provided.
For questions 37 and 38, suppose that two boys pull a sled with forces of 2.0 × 104 N at a 15° angle to the left of the center of the sled, and 1.8 × 104 N at an angle of 25° to the right of the center of the sled, respectively (see the figure).
3.6 × 104 N
_________ 37. What is the net pulling force vector on the sled?
4° to the right
Data:
Fl = 2.0 × 104 N
^ F = F 1 F
^Fx = F + Fr x = (−5170 N)+(7600 N) lrl x
F
= (2.0 ×104 N)cos(75°) l x
θl = 105°
F
≅ −5170 N
^Fx = F + Fr y = (1.93× 104 N)+(1.63× 104 N) l x l y
αl = 75°
Fr = 1.8 × 104 N
F
= (2.0 × 104 N)sin(75°) ^Fy = +3.56 ×104 N
≅ +1.93×104 N l y
^F = (+2430 N)2 +(+3.56 ×104 N)2
F
θr = 65°
αr = 65° l y
Fr x = (1.8 × 104 N)cos(65°)
^F ≅ 3.56 ×104 N (≅ 3.6 ×104 N)
+3.56 × 104 N
Fr x ≅ +7600 N
αF = tan−1 q r = 86.0° Fr y = (1.8 × 104 N)sin(65°)
Fr y ≅ +1.63×104 N
+2430 N
θF ≅ 86° (first quadrant)
3.5 × 104 N
_________ 38. If the sled does not move, what is the other force acting on the sled?
F = −F at 266° eq
Feq = −F = 3.5×104 N
θeq = 180° + 86° = 266°
F
= 3.5× 104 N at 266° eq
49 N
_________ 39. Compute the standard weight of a 5.0 kg mass.
Fw = m g
Data: m = 5.0 kg
Fw = (5.0 g) −9.81 m/s2
Fw ≅ 49.0 N (≅ 49 N) Physics Test 6: Dynamics page 5
78 N down
_________ 40. A vertical fishing line supports an 8.0 kg fish when it is held up for a picture of the “big one.” What force is exerted on the fishing line?
F = Fw = mg
Data: m = 8.0 kg
F = (8.0 kg)(−9.81 m/s2)
F ≅ −78.4 (≅ 78 N down)
In questions 41 and 42, an aircraft is landing on an aircraft carrier. The aircraft’s mass is
17 600 kg.
–41 m/s2
_________ 41. Assuming its initial horizontal landing speed is 66 m/s, what is the aircraft’s deceleration if it stops 1.6 s after catching the arresting wire with its tailhook? v2x − v1x
∆vx
Data: ax =
=
∆t ∆t m = 17 600 kg v1 x = 66 m/s
∆t = 1.6 s
0 m/s − 66 m/s ax =
1.6 s ax ≅ −41.2 m/s2 (≅ −41 m/s2)
730 000 N
_________ 42. What is the magnitude of the force that the arresting wire exerts on the aircraft, assuming that the aircraft’s deceleration is uniform?
F = max
F = (17600 kg)(41.2 m/s2)
F ≅ 725000 N (≅ 730000 N)