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HW Problems

  1. Dec 19, 2003 #1
    1) A manual specifies that certain bolts are to be tightened to a torque of 150 N/m.

    a) Using a wrench whose handle is .03 m long. what is the MINIMUM force that a technician must exert on this wrench to deliver this torque.

    b) Make a drawing to show how this is possible that the same torque could result from even a larger force using the same wrench.

    c) Explain why application of a torque like this will be more difficult for a scuba diver floating under water or an astronaut orbiting in space than it will be for a person standing on the shop floor.

    2) A driver in a 1000kg sport-utility vehicle needs to keep moving with a speed of at least 10m/s to avoid getting bogged down in sand. Entering a sand area at 20 m/s. the driver approaches a dune whose top is 10 m above her current position. The length of the trail up to the top is 100m and there is a substantial, 3000N drag force from the sand.

    how much energy must be obtained from combustion of fuel in the engine to get to the top with a speed of at least 10 m/s along this trail?

    3) A 2.0 Kg object is tied to a 3.0 m long rope so that it swings like a simple pendulum. At the lowest point in its path, the mass is moving 4.0 m/s. If we can neglect the mass of the rope and assume that the effects of swing through the air are so small they can be ignored:

    a) How high above the lowest point will this mass rise before stopping?

    b) What will be its speed when it swings back down through the lowest point on its return path?

    c) If this is set up as a demonstration, describe how measured values for A and B can be expected to compare with what was computed.

    4) A 10,000 kg railroad car is rolling freely north along a level trach at 5.0 m/s. AS it passes under a sand hopper, 30,000 kg of sand is dropped down into the car. A short time later, a hatch is opened at the bottom of the car and the sand is allowed to drain out downward.

    a) What is the momentum of the car before it is loaded?

    b) What is the momentum of the car and its load of sand?

    c) What is the momentum of the car after it is emptied?

    5) A possible origin for the material found in the rings of Saturn is a moon that got torn apart by tidal forces/

    a) Male a sketch showing a planet and use Newton's Law of Universal Gravitation to explain why tidal forces exist.

    b) Show that these forces will become greater if the moon approches the planet.

    6) a) Deescribe the condidions under which a centripetal force appears to exist.

    b) Explain how a centrifugal force could appear to exist in this situation.

    7) COnsider an Apollo program spacecraft that is approaching the moon. The command module of the spacecraft should stay in a stable orbit at an altitude of 111 km above the surface of the moon. With G - 6.67 x 10^-11N M^2/kg^2 and the Moon's mass of 7.4 x 10^22 kg and radius of about 1.7 x 10^6m.

    a) What will be the period of the command module in this orbit?

    b) If the spacecraft was traveling 40,000 km/hr during approach, was this speed fast, too slow or just right for their orbit. Explain.
  2. jcsd
  3. Dec 19, 2003 #2


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    Science Advisor

    You don't need help with a question this simple

    Apply a greater force but the force should be closer to the nut.

    A guy on a floor has a good footing. People in space or under water will just move themselves when they try to apply a force.

    summ of energies. Fd for the drag in the sand, mgh for the hill. if you have to run at 10m/s and you are going 20m/s, that means you can afford to lose 10m/s. find the energy that the suv loses from a change of 10m/s.
    fuel = Fd (sand) + mgh (hill) - (1/2)mv^2 (amount of extra kinetic energy the suv has)

    (1/2)mv^2 = mgh


    the real values will be different because true 100% efficiency does not exist.

    you don't need help to find this

    the same

    find the velocity of the cart after it was loaded with sand then multiply that velocity by the weight of the cart only.

    I can't help with that. Sorry.

    when an object is moving in a circular motion, is connected to something else and it has mass.

    The term centrifugal itself means "directed away from the axis", thus, centrifugal force means the force is pushing away from the axis. Seeing 'centrifugal' force depends on what you are refering to. Centrifugal force is exerted on whatever is the axis. The force acting on the object is centripital.

    Sorry but I can't help with these.
    Last edited: Dec 19, 2003
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