# AP Physics Lessons and Homework Torque and Universal by sanmelody

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

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?
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
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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