College Physics: A Strategic Approach (4th Edition)
4th Edition
ISBN: 9780134609034
Author: Randall D. Knight (Professor Emeritus), Brian Jones, Stuart Field
Publisher: PEARSON
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Textbook Question
Chapter 8, Problem 43P
The Achilles tendon connects the muscles in your calf to the back of your foot. When you are sprinting, your Achilles tendon alternately stretches, as you bring your weight down onto your forward foot, and contracts to push you off the ground. A 70 kg runner has an Achilles tendon that is 15 cm long and has a cross-section area of 110 mm2, typical values for a person of this size.
a. By how much will the runner’s Achilles tendon stretch if the maximum force on it is 8.0 times his weight, a typical value while running?
b. What fraction of the tendon’s length does this correspond to?
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The Achilles tendon connects the muscles in your calf to the back of your foot. When you are sprinting, your Achilles tendon alternately stretches, as you bring your weight down onto your forward foot, and contracts to push you off the ground. A 70 kg runner has an Achilles tendon that is 15 cm long with a typical 1.1 x 10-4 m2 area.a. By how much will the runner’s Achilles tendon stretch if the maximum force on it is 8.0 times his weight, a typical value while running?b. What fraction of the tendon’s length does this correspond to?
Triceps
14-
101
2.4 cm
Muscles can only contract, so they occur in pairs. In the arm, the biceps muscle is a flexor-that is, it
closes the limb. The triceps muscle is an extensor that opens the limb. This configuration is typical of
skeletal muscles, bones, and joints in humans and other vertebrates. Most skeletal muscles exert
much larger forces within the body than the limbs apply to the outside world. Imagine that a person
is pushing down on a tabletop with their hand as shown in the figure. If the person applies a
downward force of 70 N with their hand (thats about 16 lbs of force) what force does the triceps
tendon exert on the lower arm? The unknown force is indicated by the red arrow in the figure. Ignore
the weight of the arm in your calculation.
O 5.6 N
70 N
280 N
875 N
30 cm
945 N
Your answer is partially correct.
African elephants are the largest land animals. They consume approximately 10% of their body weight in food each day, which for an
adult male, can be 1000 lb. of vegetation! Their diet consists mostly of grasses, bamboo, tree bark, and fruit. They also like to dine on
tree leaves. To reach them, they often stand up on their hind legs and extend their trunks (see the figure). The elephant in the figure is
in equilibrium. The location of the elephant's center of mass is shown, and the axis of rotation has been chosen to correspond to the hip
joint. The forces in the elephant's free-body diagram are shown, and there is a static friction force between the elephant's back feet
and the ground. Use the following information and calculate the magnitude of the tension in the elephant's trunk T (m = 4540 kg, FN
= 'fs=133 cm, rcg = 76.0 cm, r = 229 cm).
Number
1103.035
+x
Axis of
rotation
Units
N
165⁰
60⁰
W
=FN
30°
FN
10°
Michael Poliza/Caters News Agency
Chapter 8 Solutions
College Physics: A Strategic Approach (4th Edition)
Ch. 8 - Prob. 1CQCh. 8 - Could a ladder on a level floor lean against a...Ch. 8 - Prob. 3CQCh. 8 - Prob. 4CQCh. 8 - Prob. 5CQCh. 8 - Prob. 6CQCh. 8 - Prob. 7CQCh. 8 - A spring exerts a 10 N force after being stretched...Ch. 8 - Prob. 9CQCh. 8 - A typical mattress has a network of springs that...
Ch. 8 - Take a spring and cut it in half to make two...Ch. 8 - A wire is stretched right to its breaking point by...Ch. 8 - Prob. 13CQCh. 8 - Prob. 14CQCh. 8 - Steel nails are rigid and unbending. Steel wool is...Ch. 8 - Two children hold opposite ends of a lightweight,...Ch. 8 - Prob. 19MCQCh. 8 - Prob. 20MCQCh. 8 - Prob. 21MCQCh. 8 - Prob. 22MCQCh. 8 - Prob. 23MCQCh. 8 - Prob. 24MCQCh. 8 - Prob. 25MCQCh. 8 - Prob. 26MCQCh. 8 - You have a heavy piece of equipment hanging from a...Ch. 8 - Prob. 1PCh. 8 - Prob. 2PCh. 8 - Prob. 3PCh. 8 - Prob. 4PCh. 8 - Youre carrying a 3.6-m-long, 25 kg pole to a...Ch. 8 - Prob. 6PCh. 8 - Prob. 7PCh. 8 - Prob. 9PCh. 8 - Prob. 11PCh. 8 - Prob. 13PCh. 8 - Prob. 14PCh. 8 - Prob. 15PCh. 8 - The stability of a vehicle is often rated by the...Ch. 8 - Prob. 18PCh. 8 - A car manufacturer claims that you can drive its...Ch. 8 - Prob. 20PCh. 8 - An orthodontic spring, connected between the upper...Ch. 8 - Prob. 22PCh. 8 - Experiments using optical tweezers measure the...Ch. 8 - Prob. 24PCh. 8 - One end of a 10-cm-long spring is attached to the...Ch. 8 - Prob. 26PCh. 8 - A spring has an unstretched length of 10 cm. It...Ch. 8 - A spring stretches 5.0 cm when a 0.20 kg block is...Ch. 8 - You need to make a spring scale to measure the...Ch. 8 - Prob. 30PCh. 8 - A force stretches a wire by 1.0 mm. a. A second...Ch. 8 - Prob. 32PCh. 8 - What hanging mass will stretch a 2.0-m-long,...Ch. 8 - An 80-cm-long, 1.0-mm-diameter steel guitar string...Ch. 8 - A mineshaft has an ore elevator hung from a single...Ch. 8 - The normal force of the ground on the foot can...Ch. 8 - A three-legged wooden bar stool made out of solid...Ch. 8 - Prob. 38PCh. 8 - Prob. 39PCh. 8 - Prob. 40PCh. 8 - A glass optical fiber in a communications system...Ch. 8 - The Achilles tendon connects the muscles in your...Ch. 8 - Prob. 44PCh. 8 - Prob. 47PCh. 8 - Prob. 48PCh. 8 - Prob. 49PCh. 8 - Prob. 51GPCh. 8 - Prob. 52GPCh. 8 - Prob. 53GPCh. 8 - Prob. 55GPCh. 8 - Two identical, side-by-side springs with spring...Ch. 8 - Prob. 57GPCh. 8 - Prob. 58GPCh. 8 - Prob. 59GPCh. 8 - A 25 kg child bounces on a pogo stick. The pogo...Ch. 8 - Prob. 61GPCh. 8 - In the hammer throw, an athlete spins a heavy mass...Ch. 8 - There is a disk of cartilage between each pair of...Ch. 8 - Orb spiders make silk with a typical diameter of...Ch. 8 - Larger animals have sturdier bones than smaller...Ch. 8 - Prob. 67GPCh. 8 - Prob. 68GPCh. 8 - Prob. 69MSPPCh. 8 - Prob. 70MSPPCh. 8 - Prob. 71MSPPCh. 8 - Prob. 72MSPP
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- African elephants are the largest land animals. They consume approximately 10% of their body weight in food each day, which for an adult male, can be 1000 lb. of vegetation! Their diet consists mostly of grasses, bamboo, tree bark, and fruit. They also like to dine on tree leaves. To reach them, they often stand up on their hind legs and extend their trunks (see the figure). The elephant in the figure is in equilibrium. The location of the elephant's center of mass is shown, and the axis of rotation has been chosen to correspond to the hip joint. The forces in the elephant's free-body diagram are shown, and there is a static friction force between the elephant's back feet and the ground. Use the following information and calculate the magnitude of the tension in the elephant's trunk T (m = 4540 kg, FN = rfs = 133 cm, rcg = 76.0 cm, r = 229 cm). Number +x Axis of rotation Units 60 165 30 W TTFN cg 10° Michael Poliza/Caters News Agencyarrow_forwardThe uniform beam has a mass of 46 kg per meter of length. Determine the reactions at the supports. A umber of significant digits is 3. The tolerance is ± 1 in the nificant digit. A₂= i Bio By= 2.9 m i N !N N 1.4 m- 300 kg Barrow_forwardA Foucault pendulum in a physics department (used to prove that the earth rotates) consists of a 120 kg steel ball that swings at the end of a 6.0-m-long steel cable. The cable has a diameter of 2.5 mm. When the ball was first hung from the cable, by how much did the cable stretch?arrow_forward
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