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posted by  Maxie on 11/7/2009 12:46:09 PM  |  status: Live  |  Earned Karma: 25

LIFESAVER Exam Monday.....solids and fluids

Course Textbook Chapter Problem Needs by
General Physics N/A N/A N/A 11/7/2009 at 6:00:00 PM
Question Details:
SOLIDS AND FLUIDS

A)If the elastic limit of steel is 5.0 multiplied by 108 Pa, determine the minimum diameter a steel wire can have if it is to support a 73-kg circus performer without its elastic limit being exceeded.
1 mm

B)For safety in climbing, a mountaineer uses a nylon rope that is 55 m long and 1.1 cm in diameter. When supporting a 96-kg climber, the rope elongates 2.0 m. Find its Young's modulus.
1 Pa

C)Bone has a Young's modulus of about
1.80 1010 Pa. Under compression, it can withstand a stress of about 1.60 108 Pa before breaking. Assume that a femur (thigh-bone) is 0.42 m long, and calculate the amount of compression this bone can withstand before breaking.
1 mm

D)A large man sits on a four-legged chair with his feet off the floor. The combined mass of the man and chair is 95.0 kg. If the chair legs are circular and have a radius of 0.400 cm at the bottom, what pressure does each leg exert on the floor?
1 Pa

E)The four tires of an automobile are inflated to a gauge pressure of 2.1 105 Pa. Each tire has an area of 0.022 m2 in contact with the ground. Determine the weight of the automobile.
1 N
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Oracle
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posted by Golden Monkey on 11/7/2009 2:19:20 PM  |  status: Live
Asker's Rating: Somewhat Helpful   
Response Details:
(a)  limit  =  force / area 
.
    L  =  mg  /  (π d2 / 4)
.
     d2  =  4mg / π L  =   4 * 73 * 9.8 / π * 5.0 x 108 /  =   18.217 x 10-6 
.
    d  =    4.27 mm
The Israelites angered the lord when they worshipped the golden calf. They should have worshipped the GOLDEN MONKEY instead!
Oracle
Karma Points: 87,981
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posted by Golden Monkey on 11/7/2009 2:23:24 PM  |  status: Live
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Response Details:
B)For safety in climbing, a mountaineer uses a nylon rope that is 55 m long and 1.1 cm in diameter. When supporting a 96-kg climber, the rope elongates 2.0 m. Find its Young's modulus.
.
Youngs mod  =  stress / strain   =  (force / area)  /  (ΔL / L)
.
   Y  =  mg L  /  (πd2/4) ΔL  =   4mgL / πd2 ΔL  =
.
            =  4 * 96 * 9.80 * 55  /  π* 0.0112 * 2.0   =     2.72 x 108  Pa
The Israelites angered the lord when they worshipped the golden calf. They should have worshipped the GOLDEN MONKEY instead!
Oracle
Karma Points: 87,981
(Ecole Polytechnique Fédérale de Lausanne)
posted by Golden Monkey on 11/7/2009 2:25:57 PM  |  status: Live
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Response Details:
C)Bone has a Young's modulus of about
1.80 1010 Pa. Under compression, it can withstand a stress of about 1.60 108 Pa before breaking. Assume that a femur (thigh-bone) is 0.42 m long, and calculate the amount of compression this bone can withstand before breaking.
.
stress  =  Y  * strain
.
 stress  =  Y *  ΔL  / L
.
  ΔL  =  L * stress / Y  =  0.42 * 1.60 x 108 / 1.80 x 1010  =    0.00373 meters  =    3.73 mm
The Israelites angered the lord when they worshipped the golden calf. They should have worshipped the GOLDEN MONKEY instead!
Oracle
Karma Points: 87,981
(Ecole Polytechnique Fédérale de Lausanne)
posted by Golden Monkey on 11/7/2009 2:28:58 PM  |  status: Live
Asker's Rating: Somewhat Helpful   
Response Details:
D)A large man sits on a four-legged chair with his feet off the floor. The combined mass of the man and chair is 95.0 kg. If the chair legs are circular and have a radius of 0.400 cm at the bottom, what pressure does each leg exert on the floor?
.
 Area of each leg  =  π r2  =  π * 0.0042  =   50.2656 x 10-6  m2
.
Force on each leg  =  1/4  of total weight  =  1/4  *  mg  =  1/4 * 95 * 9.80  =  232.75 newtons
.
Pressure  on each leg  =  force / area  =  232.75 / 50.2656 x 10-6   =     4.63 x 106  Pa
The Israelites angered the lord when they worshipped the golden calf. They should have worshipped the GOLDEN MONKEY instead!
Oracle
Karma Points: 87,981
(Ecole Polytechnique Fédérale de Lausanne)
posted by Golden Monkey on 11/7/2009 2:30:49 PM  |  status: Live
Asker's Rating: Helpful   
Response Details:
E)The four tires of an automobile are inflated to a gauge pressure of 2.1 105 Pa. Each tire has an area of 0.022 m2 in contact with the ground. Determine the weight of the automobile.
.
Force from each tire  =  pressure * area  =  2.10 x 105 * 0.022  =    4620 Newtons
.
weight of car  =  force from all four tires  =  4 * 4620  =   18480 Newtons
The Israelites angered the lord when they worshipped the golden calf. They should have worshipped the GOLDEN MONKEY instead!
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