College Physics: A Strategic Approach (3rd Edition)
3rd Edition
ISBN: 9780321879721
Author: Randall D. Knight (Professor Emeritus), Brian Jones, Stuart Field
Publisher: PEARSON
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Chapter 8, Problem 5CQ
To determine
To explain: The cause for the extension of arms by the divers in front of them.
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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 Agency
When you carry shopping bags, rather than grasp the handles with your hand as in Q8.14a, you might choose to put them over your arm and slide the handle toward your elbow as in Q8.14b. Explain why this leads to less muscle effort to carry the bags and less force in your elbow joint.
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 (3rd Edition)
Ch. 8 - An object is acted upon by two (and only two)...Ch. 8 - Prob. 2CQCh. 8 - Could a ladder on a level floor lean against a...Ch. 8 - If you are using a rope to raise a tall mast,...Ch. 8 - Prob. 5CQCh. 8 - Prob. 6CQCh. 8 - Prob. 7CQCh. 8 - A spring exerts a 10 N force after being stretched...Ch. 8 - The left end of a spring is attached to a wall....Ch. 8 - A spring is attached to the floor and pulled...
Ch. 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 - Steel nails are rigid and unbending. Steel wool is...Ch. 8 - The rod in Figure Q8.15 pivots around an axle at...Ch. 8 - Two children hold opposite ends of a lightweight,...Ch. 8 - Prob. 17MCQCh. 8 - Prob. 18MCQCh. 8 - Prob. 19MCQCh. 8 - Prob. 20MCQCh. 8 - Prob. 21MCQCh. 8 - Prob. 22MCQCh. 8 - You have a heavy piece of equipment hanging from a...Ch. 8 - Prob. 24MCQCh. 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 - How much torque must the pin exert to keep the rod...Ch. 8 - Prob. 8PCh. 8 - Prob. 9PCh. 8 - Consider the procedure for measuring a womans...Ch. 8 - Prob. 11PCh. 8 - Prob. 12PCh. 8 - Prob. 13PCh. 8 - Prob. 14PCh. 8 - Prob. 15PCh. 8 - Prob. 16PCh. 8 - Prob. 17PCh. 8 - The stability of a vehicle is often rated by the...Ch. 8 - You want to slowly push a stiff board across a 20...Ch. 8 - Prob. 20PCh. 8 - A car manufacturer claims that you can drive its...Ch. 8 - Prob. 22PCh. 8 - One end of a spring is attached to a wall. A 25 N...Ch. 8 - An orthodontic spring, connected between the upper...Ch. 8 - Experiments using optical tweezers measure the...Ch. 8 - A spring has an unstretched length of 10 cm. It...Ch. 8 - One end of a 10-cm-long spring is attached to the...Ch. 8 - A spring stretches 5.0 cm when a 0.20 kg block is...Ch. 8 - A 1.2 kg block is hung from a vertical spring,...Ch. 8 - You need to make a spring scale to measure the...Ch. 8 - A force stretches a wire by 1.0 mm. a. A second...Ch. 8 - What hanging mass will stretch a 2.0-m-long,...Ch. 8 - How much force does it take to stretch a...Ch. 8 - An 80-cm-long, 1.0-mm-diameter steel guitar string...Ch. 8 - A student is testing a 1.0 m length of...Ch. 8 - A 1.2-m-long steel rod with a diameter of 0.50 cm...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. 40PCh. 8 - A glass optical fiber in a communications system...Ch. 8 - The Achilles tendon connects the muscles in your...Ch. 8 - Prob. 43GPCh. 8 - Prob. 44GPCh. 8 - Using the information in Figure 8.2, calculate the...Ch. 8 - A woman weighing 580 N does a pushup from her...Ch. 8 - Prob. 47GPCh. 8 - Prob. 48GPCh. 8 - Prob. 49GPCh. 8 - The wheel of mass m in Figure P8.50 is pulled on...Ch. 8 - A 5.0 kg mass hanging from a spring scale is...Ch. 8 - Two identical, side-by-side springs with spring...Ch. 8 - Two springs have the same equilibrium length but...Ch. 8 - Figure P8.54 shows two springs attached to a block...Ch. 8 - A 60 kg student is standing atop a spring in an...Ch. 8 - A 25 kg child bounces on a pogo stick. The pogo...Ch. 8 - Figure P8.57 shows a lightweight plank supported...Ch. 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 - In Example 8.1, the tension in the biceps tendon...Ch. 8 - Larger animals have sturdier bones than smaller...Ch. 8 - Orb spiders make silk with a typical diameter of...Ch. 8 - Prob. 63MSPPCh. 8 - Prob. 64MSPPCh. 8 - Prob. 65MSPP
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- BIO When a gymnast performing on the rings executes the iron cross, he maintains the position at rest shown in Figure P10.85a. In this maneuver, the gymnasts feet (not shown) are off the floor. The primary muscles involved in supporting this position are the latissimus dorsi (lats) and the pectoralis major (pecs). One of the rings exerts an upward fore Fh on a hand as shown in Figure P10.85b. The force Fs is exerted by the shoulder joint on the arm. The latissimus dorsi and pectoralis major muscles exert a total force Fm on the arm. (a) Using the information in the figure, find the magnitude of the force Fm. (b) Suppose an athlete in training cannot perform the iron cross but can hold a position similar to the figure in which the arms make a 45 angle with the horizontal rather than being horizontal. Why is this position easier for the athlete? Figure P10.85arrow_forwardA bench is made by placing a 3.9 meter long plank on two legs, each 0.36 meters from one of the plank's ends. The plank has a mass of 7.5 kg. If a box is placed on one of the ends of the plank, what is the maximum mass the box can have before it tips the bench over?arrow_forwardWhen you bend your knee, the quadriceps muscle is stretched. This increases the tension in the quadriceps tendon attached to your kneecap (patella), which, in turn, increases the tension in the patella tendon that attaches your kneecap to your lower leg bone (tibia). Simultaneously, the end of your upper leg bone (femur) pushes outward on the patella. Shown is how these parts of a knee joint are arranged. What size force does the femur exert on the kneecap if the tendons are oriented as in the figure and the tension in each tendon is 60 N?arrow_forward
- Figure P10.31 shows a claw hammer being used to pull a nail out of a horizontal board. The mass of the hammer is 1.00 kg. A force of 150 N is exerted horizontally as shown, and the nail does not yet move relative to the board. Find (a) the force exerted by the hammer claws on the nail and (b) the force exerted by the surface on the point of contact with the hammer head. Assume the force the hammer exerts on the nail is parallel to the nail. Figure P10.31arrow_forwardChildren playing pirates have suspended a uniform wooden plank with mass 15.0 kg and length 2.50 m as shown in Figure P14.27. What is the tension in each of the three ropes when Sophia, with a mass of 23.0 kg, is made to walk the plank and is 1.50 m from reaching the end of the plank? FIGURE P14.27arrow_forwardConsider the shelf in the figure. Suppose all supports fail and only O is working properly; if the shelf does not move, what must be the mass of the flowerpot on the left?arrow_forward
- You’re carrying a 3.6-m-long, 25 kg pole to a construction site when you decide to stop for a rest. You place one end of the pole on a fence post and hold the other end of the pole 35 cm from its tip. How much force must you exert to keep the pole motionless in a horizontal position?arrow_forwardA refrigerator of width w and height h rests on a rough incline as in Figure P8.25. Find an expression for the maximum value 0 can have before the refrigerator tips over. Note, the contact point between the refrigerator and incline shifts as 0 increases and treat the refrigerator as a uniform box.arrow_forward?arrow_forward
- A uniform 10.0 m beam of mass 300 kg extends over a ledge, as in Figure. The beam is not attached but simply rests on the surface. A 60.0 kg student intends to position the beam so that he can walk to the end of it. What is the maximum distance the beam can extend past the end of the ledge and still allow him to perform this feat?arrow_forwardA board 2 meters long weighing 100 N is hanging off the edge of a table. The center of mass of the board is at its center and is 0.2 m from the edge. Can a 20 N cat climb out to the end of the board without it falling? Yes No Not enough informationarrow_forwardA74 kg window cleaner uses a 15 kg ladder that is 6.7 m long. He places one end on the ground 3.0 m from a wall, rests the upper end against a cracked window, and climbs the ladder. He is 3.5 m up along the ladder when the window breaks, Neglect friction between the ladder and window and assume that the base of the ladder does not slip. When the window is on the verge of breaking, what are (a) the magnitude of the force on the window from the ladder, (b) the magnitude of the force on the ladder from the ground, and (c) the angle (relative to the horizontal) of that force on the ladder? (a) Number Units (b) Number Units (c) Number Unitsarrow_forward
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