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P112 Spring 2007
Homework #11
Due: Friday April 13th, 2007 – At lecture
Reading: 11.111.3, 10.410.7
Not all concepts will be covered in class – you are responsible
for all material in the reading and in the homework problems.
Warmup Exercises:
(Answer only will be marked)
1.
A solid wood door 1.00 m wide and 2.00 m high is
hinged along one side and has a total mass 40.0 kg.
Initially open and at rest, the door is struck at its
center by a handful of sticky mud with mass 0.500 kg,
traveling perpendicular to the door at 12.0 m/s just
before impact. Find the angular speed of the door.
Does the mud make a significant contribution to the
moment of inertia?
2.
See Figure 11.43 in your Text Book. A gate 4.00 m
wide and 2.00 m high weighs 500 N. Its center of
gravity is at its center, and it is hinged at A and B. To
relieve the strain on the top hinge, a wire is connected
from C to D, as shown in the Figure. The tension in
CD is increased until the horizontal force at hinge A
is zero.
a) what is the tension in the wire CD?
b) what is the magnitude of the horizontal component
of the force at hinge B?
c) what is the combined vertical force exerted by
hinges A and B?
Mathematics Exercises:
3.
Find a vector which is perpendicular to both
u=(3,0,2) and v=(1,1,1)
Estimation:
(Marked based solely on logic)
4.
Estimate the tension in the metal suspension rods
of the Golden Gate Bridge in San Francisco.
Problems:
5.
A ladder 5.0 m long rests against a frictionless
vertical wall with its lower end 3.0 m from the wall.
The ladder weighs 160 N. The coefficient of static
friction between the foot of the ladder and the ground
is 0.40. A man weighing 740 N climbs slowly up the
ladder.
a) What is the maximum frictional force that the
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 Spring '07
 LECLAIR,A
 mechanics, Work

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