AP Physics Lessons and Homework Torque and Universal by sanmelody


									                     AP Physics                  Name:
                     Lessons 9 and 10 Homework
                     Torque and Universal        Date:

1.   A uniform meterstick pivoted
     at its center has a 100g mass
     suspended at the 25.0 cm
     position. (a) At what position
     should a 75.0g mass be placed
     to put the system in
     equilibrium? (b) What mass
     would have to be placed at the
     90.0cm position for the system
     to be in equilibrium?
2.   The pedals of a bicycle rotate
     in a circle with a diameter of
     40 cm. What is the maximum
     torque a 55kg rider can apply
     by putting all of her weight on
     one pedal?
3.   A 20kg ladder of 3.0m length
     is placed at a 80o angle against
     a wall. What is the frictional
     force that has to act on the
     bottom of the ladder to keep it
     from slipping?
4.   A painter of 75kg mass is
     standing on a rung two thirds
     up from the bottom of the
     ladder that was described in 2.
     How much friction has to act
     on the bottom of the ladder to
     keep it from slipping?
5.   Telephone and electrical lines
     are allowed to sag between the
     poles so that the tension will
     not be too great when
     something hits or sits on the
     line. (a) Is it possible for the
     lines to be perfectly horizontal?
     Justify your answer. (b)
     Suppose that the lines would
     sag only 0.10 m exactly
     halfway between the poles that
     are 30 m apart. If a 0.25 kg bird
      sits on the wire midway
      between the poles and you
      would ignore the mass of the
      wire itself, what would be the
      tension in the wire?
6.    What is the acceleration due to
      gravity on top of Mt. Everest?
      The summit is about 8.80 km
      above sea level.
7.    For a spacecraft going directly
      from the Earth to the Moon,
      beyond what point will lunar
      gravity dominate? Are the
      astronauts onboard a spacecraft
      at this point truly weightless?
8.    Two inquisitive physics
      students arranged for a high
      jump competition at the
      summit of Mt. Everest. At sea
      level they are able to elevate
      their center of gravity 1.20 m
      during a high jump. How much
      elevation would their center of
      gravity experience on Mt.
      Everest. Neglect differences in
      air density and the additional
      gear they might have to wear.
9.    Two objects are attracting each
      other with a certain
      gravitational force. (a) How
      would the force between the
      objects change if they were
      placed at a distance 3 times the
      original? (b) How would you
      have to change the masses to
      keep the gravitational force the
      same as the original.
10.   A 75 kg man weighs 735N on
      the surface of Earth. How far
      above the surface of the Earth
      would he have to go to “lose”
      10% of his body weight?
11.   Four identical masses of 2.5 kg
      each are located at the corners
      of a square with 1.0 m sides.
      What is the net force on any
one of the masses? Where
would the net gravitational
force be zero?

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