Physics

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Author:
thinkrussia
ID:
175039
Filename:
Physics
Updated:
2012-10-02 13:45:39
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homework
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homework 4
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  1. Which one of the following objects is in equilibrium?

    A race horse taking off at the beginning of a race.
    A taxi coming to a halt to discharge a passenger.    
    A space probe with its engines shut down, moving through a vast empty region of outer space.
    A projectile as it passes through the topmost point of its trajectory.
    A brick falling from a bridge.
    A space probe with its engines shut down, moving through a vast empty region of outer space.
  2. A certain object is in equilibrium. Which one of the following statements is not true?

    The object must be at rest.
    No net force acts on the object.    
    The object has no acceleration.
    The object has a constant velocity.
    The object must be at rest.
  3. A certain object is not in equilibrium. Three of the following
    statements could possibly be true, and one must be true. Which one of
    the following must be true?

    A net force acts on the object.
    Only three forces act on the object.    
    Only two perpendicular forces act on the object.
    Only a single force acts on the object.
    A net force acts on the object.
  4. Three forces act on a moving object. One force has a magnitude of 82.0 N and is directed due north. Another has a magnitude of 58.0N and is directed due west. What must be the magnitude and direction of the third force, such that the object continues to move with a constant velocity?


    magnitude ____ N
    direction _____° south of east
    • magnitude 100.44 N
    • direction 54.7° south of east
  5. The drawing shows a wire tooth brace used by orthodontists. The topmost tooth is protruding slightly, and the tension in the wire exerts two forces and ' on this tooth in order to bring it back into alignment. If the forces have the same magnitude of 13.0 N, what is the magnitude of the net force exerted on the tooth by these forces? (16 degrees on both sides)
    ____N
    7.17N
  6. A mountain climber, in the process of crossing between two cliffs by a rope, pauses to rest. She weighs 526 N. As the drawing shows, she is closer to the left cliff than to the right cliff, with the result that the tensions in the left and right sides of the rope are not the same. Find the tensions in the rope to the left and to the right of the mountain climber. (From the figure α = 71.0° and β = 83.0°.)

    TL = _______N
    TR =_______N
    TL = 1190.95N TR = 1134.52N
  7. A fisherman is fishing from a bridge and is using a "35-N test line." In other words, the line will sustain a maximum force of 35N without breaking. What is the weight of the heaviest fish that can be pulled up vertically when the line is reeled in the following situations?

    (a) at a constant speed
    ____N
    (b) with an acceleration whose magnitude is 1.9 m/s2
    ____N
    • (a) at a constant speed 35N
    • (b) with an acceleration whose magnitude is 1.9 m/s2 29.3N
  8. A helicopter flies over the arctic ice pack at a constant altitude, towing an airborne 135-kg laser sensor that measures the thickness of the ice (see the drawing). The helicopter and the sensor both move only in the horizontal direction and have a horizontal acceleration of magnitude 2.85 m/s2. Ignoring air resistance, find the tension in the cable towing the sensor.
    _____N
    1377.8N
  9. In a supermarket parking lot, an employee is pushing ten empty shopping carts, lined up in a straight line. The acceleration of the carts is 0.055 m/s2. The ground is level, and each cart has a mass of 31 kg.

    (a) What is the net force acting on any one of the carts? ____N
    (b) Assuming friction is negligible, what is the force exerted by the fifth cart on the sixth cart?_____N
    • (a) What is the net force acting on any one of the carts? 1.7N
    • (b) Assuming friction is negligible, what is the force exerted by the fifth cart on the sixth cart? 8.525N
  10. In the drawing, the weight of the block on the table is 498 N and that of the hanging block is 175 N. Ignore all frictional effects, and assuming the pulley to be massless.

    (a) Find the acceleration of the two blocks. _____m/s2
    (b) Find the tension in the cord. _____N
    (a) Find the acceleration of the two blocks. 2.55m/s2 (b) Find the tension in the cord. 129.4N
  11. A student is skateboarding down a ramp that is 5.4 m long and inclined at 25° with respect to the horizontal. The initial speed of the skateboarder at the top of the ramp is 2.1 m/s. Neglect friction and find the speed at the bottom of the ramp.
    _____m/s
    7m/s
  12. A man seeking to set a world record wants to tow a 116,000-kg airplane along a runway by pulling horizontally on a cable attached to the airplane. The mass of the man is 79 kg, and the coefficient of static friction between his shoes and the runway is 0.75. What is the greatest acceleration the man can give the airplane? Assume that the airplane is on wheels that turn without any frictional resistance.
    _____m/s2
    .005m/s2

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