This preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis is an unformatted preview. Sign up to view the full document.
View Full DocumentCHAPTER 12 Static Equilibrium and Elasticity 1* True or false: ( a ) F = 0 is sufficient for static equilibrium to exist. ( b ) F = 0 is necessary for static equilibrium to exist. ( c ) In static equilibrium, the net torque about any point is zero. ( d ) An object is in equilibrium only when there are no forces acting on it. ( a ) False ( b ) True ( c ) True ( d ) False 2 A seesaw consists of a 4-m board pivoted at the center. A 28-kg child sits on one end of the board. Where should a 40-kg child sit to balance the seesaw? Apply t = 0 about the pivot 2 28 = 40 d ; d = 1.4 m from pivot 3 In Figure 12-23, Misako is about to do a push-up. Her center of gravity lies directly above point P on the floor, which is 0.9 m from her feet and 0.6 m from her hands. If her mass is 54 kg, what is the force exerted by the floor on her hands? Apply t = 0 about her feet as a pivot 0.9 54 9.81 = F 1.5 N . m; F = 318 N 4 Juan and Bettina are carrying a 60-kg block on a 4-m board as shown in Figure 12-24. The mass of the board is 10 kg. Since Juan spends most of his time reading cookbooks, whereas Bettina regularly does push-ups, they place the block 2.5 m from Juan and 1.5 m from Bettina. Find the force in newtons exerted by each to carry the block. Apply t = 0 about the right end of the board Apply F = 0 (60 1.5 + 10 2) g = 4 F J ; F J = 270 N 70 g = 270 N + F B ; F B = 417 N 5* Misako wishes to measure the strength of her biceps muscle by exerting a force on a test strap as shown in Figure 12-25. The strap is 28 cm from the pivot point at the elbow, and her biceps muscle is attached at a point 5 cm from the pivot point. If the scale reads 18 N when she exerts her maximum force, what force is exerted by the biceps muscle? Apply t = 0 about the pivot 28 18 = 5 F ; F = 101 N 6 A crutch is pressed against the sidewalk with a force F c along its own direction as in Figure 12-26. This force is balanced by the normal force F n and a frictional force f s . ( a ) Show that when the force of friction is at its maximum value, the coefficient of friction is related to the angle q by m s = tan q . ( b ) Explain how this result applies to the forces Chapter 12 Static Equilibrium and Elasticity on your foot when you are not using a crutch. ( c ) Why is it advantageous to take short steps when walking on ice? ( a ) f s,max = m s F n ; F n = F c cos q . For equilibrium, f s = F c sin q . If f s = f s,max = F c sin q = m s F c cos q , m s = tan q . ( b ) Taking long strides requires a large coefficient of static friction because q is then large. ( c ) If m s is small, i.e., there is ice on the surface, q must be small to avoid slipping. ... View Full Document
This preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentChapter 2
Ch1
Chapter 11
Chapter 5
Chapter 25F
Chapter 18F
anschp05
PHYS 107 Homework 8 Solutions
Ch12
ch12f
lecture13_tth_2101_S11
10.1 Physics 6A Torque
Copyright © 2015. Course Hero, Inc.
Course Hero is not sponsored or endorsed by any college or university.