A Grand Entrance You are designing an apparatus to support an actor of mass 80.0 kg who is to "fly" down to the stage during the performance of a play. You attach the actor's harness to a 150 kg sandbag by means of a lightweight steel cable running smoothly over two frictionless pulleys as in figure (a). You need 3.75 m of cable between the harness and the nearest pulley so that the pulley can be hidden behind a curtain. For the apparatus to work successfully, the sandbag must never lift above the floor as the actor swings from above the stage to the floor. Let us call the initial angle that the actor's cable makes with the vertical 0. What is the maximum value ở can have before the sandbag lifts off the floor? (a) An actor uses some dever staging to make s entrance. (b) The free-body diagram for the actor at the bottom of the circular path. (c) The free-body diagram for the sandbag if the normal force from the floor goes to zero. Macor ag Actor Sandbag mactor a SOLUTION Conceptualize We must use several concepts to solve this problem. Imagine what happens as the actor approaches the bottom of the swing. At the bottom, the cable is ---Select-- v and must support his weight as well as provide centripetal acceleration of his body in the upward direction. At this point in his swing, the tension in the cable is the highest and the sandbag is most likely to lift off the floor. Categorize Looking first at the swinging of the actor from the initial point to the lowest point, we model the actor and the Earth as an isolated system. We ignore air resistance, so there are no ---Select--- v forces acting. You might initially be tempted to model the system as nonisolated because of the interaction of the system with the cable, which is in the environment. The force applied to the actor by the cable, however, is always perpendicular to each element of the displacement of the actor and hence does no work. Therefore, in terms of energy transfers across the boundary, the system is isolated. Analyze We first find the actor's speed as he arrives at the floor as a function of the initial angle e and the radius R of the circular path through which he swings. From the isolated system model, make the appropriate reduction of the fully expanded conservation of energy equation for the ---Select--- v system: AK + AU, -0 Let y, be the initial height of the actor above the floor and v,, be his speed at the instant before he lands. (Notice that K, -0 because the actor starts from rest and that U,- O because we define the configuration of the actor at the floor as having a gravitational potential energy of zero. Use the following as necessary: mactor Ve 9, R, and y. Do not substitute numerical values; use variables only.) -)-(-- (1) From the geometry in figure (a), notice that y, - 0, so y,- R - R cos(0) - R(1 - cos(0)). Use this relationship in Equation (1) and solve for v. (Use the following as necessary: g, mactor and R. Do not substitute numerical values; use variables only.) (2) v - Categorize Next, focus on the instant the actor is at the lowest point. Because the tension in the cable is transferred as a force applied to the sandbag, we model the actor at this instant as a particle ---Select--- Because the actor moves along a circular arc, he experiences at the bottom of the swing a centripetal acceleration of directed upward. Analyze Apply Newton's second law from the particle under a net force model to the actor at the bottom of his path, using the free-body diagram in figure (b) as a guide, and recognizing the acceleration as centripetal. (Use the following as necessary: R, g, and v, Do not substitute numerical values; use variables only.) v? SF,-T- mactor9 - mactor mactor (3) T- Categorize Finally, notice that the sandbag lifts off the floor when the upward force exerted on it by the cable ---Select--- v the gravitational force acting on it; the normal force from the floor is zero when that happens. We do not, however, want the sandbag to lift off the floor. The sandbag must remain at rest, so we model it as a particle in equilibrium. Analyze A force T of the magnitude given by Equation (3) is transmitted by the cable to the sandbag. If the sandbag remains at rest but is just ready to be lifted off the floor if any more force were applied by the cable, the normal force on it becomes zero and the particle in equilibrium model tells us that T? v mpagg as in figure (c). Substitute this condition and Equation (2) into Equation (3): 2gR(1 - cos(0)) mpagg - mactor9g + mactor- Solve for cos(0) and substitute the given parameters, then solve for (in degrees) (Due to the nature of this problem, do not use rounded intermediate values in your calculations-including answers submitted in WebAssign.): 3mactor- moag. 2mactor 1. cos(e) - Finalize Here we had to combine several analysis models from different areas of our study. Notice that the length R of the cable from the actor's harness to the leftmost pulley did not appear in the final algebraic equation for cos(0). Therefore, the final answer is independent of which of the following? O mactor OR O mpag EXERCISE The director and his staff forget it is the body-double stuntman who is flying, not the actor. The stuntman's mass is 14 kg more than the actor. At the last second, you are asked to calculate how much extra mass, AM (in kg), to add to the sandbag in order to maintain the same maximum angle (Due to the nature of this problem, do not use rounded intermediate values in your calculations-including answers submitted in WebAssign.) Hint kg Need Help? Read It

Structural Analysis
6th Edition
ISBN:9781337630931
Author:KASSIMALI, Aslam.
Publisher:KASSIMALI, Aslam.
Chapter2: Loads On Structures
Section: Chapter Questions
Problem 1P
icon
Related questions
Question
A Grand Entrance
You are designing an apparatus to support an actor of mass 80.0 kg who is to "fly" down to the stage during the performance of a play. You attach the actor's harness to a 150 kg sandbag by means of a lightweight steel cable
running smoothly over two frictionless pulleys as in figure (a). You need 3.75 m of cable between the harness and the nearest pulley so that the pulley can be hidden behind a curtain. For the apparatus to work successfully, the
sandbag must never lift above the floor as the actor swings from above the stage to the floor. Let us call the initial angle that the actor's cable makes with the vertical 0. What is the maximum value ở can have before the sandbag
lifts off the floor?
(a) An actor uses some dever staging to make
s entrance.
(b) The free-body diagram for the actor at the bottom of the circular
path. (c) The free-body diagram for the sandbag if the normal force
from the floor goes to zero.
Macor
ag
Actor
Sandbag
mactor
a
SOLUTION
Conceptualize We must use several concepts to solve this problem. Imagine what happens as the actor approaches the bottom of the swing. At the bottom, the cable is ---Select-- v and must support his weight as well as provide
centripetal acceleration of his body in the upward direction. At this point in his swing, the tension in the cable is the highest and the sandbag is most likely to lift off the floor.
Categorize Looking first at the swinging of the actor from the initial point to the lowest point, we model the actor and the Earth as an isolated system. We ignore air resistance, so there are no ---Select---
v forces acting. You
might initially be tempted to model the system as nonisolated because of the interaction of the system with the cable, which is in the environment. The force applied to the actor by the cable, however, is always perpendicular to each
element of the displacement of the actor and hence does no work. Therefore, in terms of energy transfers across the boundary, the system is isolated.
Analyze We first find the actor's speed as he arrives at the floor as a function of the initial angle e and the radius R of the circular path through which he swings.
From the isolated system model, make the appropriate reduction of the fully expanded conservation of energy equation for the ---Select---
v system:
AK + AU, -0
Let y, be the initial height of the actor above the floor and v,, be his speed at the instant before he lands. (Notice that K, -0 because the actor starts from rest and that U,- O because we define the configuration of the actor at the
floor as having a gravitational potential energy of zero. Use the following as necessary: mactor Ve 9, R, and y. Do not substitute numerical values; use variables only.)
-)-(--
(1)
From the geometry in figure (a), notice that y, - 0, so y,- R - R cos(0) - R(1 - cos(0)). Use this relationship in Equation (1) and solve for v. (Use the following as necessary: g, mactor and R. Do not substitute numerical values;
use variables only.)
(2) v -
Transcribed Image Text:A Grand Entrance You are designing an apparatus to support an actor of mass 80.0 kg who is to "fly" down to the stage during the performance of a play. You attach the actor's harness to a 150 kg sandbag by means of a lightweight steel cable running smoothly over two frictionless pulleys as in figure (a). You need 3.75 m of cable between the harness and the nearest pulley so that the pulley can be hidden behind a curtain. For the apparatus to work successfully, the sandbag must never lift above the floor as the actor swings from above the stage to the floor. Let us call the initial angle that the actor's cable makes with the vertical 0. What is the maximum value ở can have before the sandbag lifts off the floor? (a) An actor uses some dever staging to make s entrance. (b) The free-body diagram for the actor at the bottom of the circular path. (c) The free-body diagram for the sandbag if the normal force from the floor goes to zero. Macor ag Actor Sandbag mactor a SOLUTION Conceptualize We must use several concepts to solve this problem. Imagine what happens as the actor approaches the bottom of the swing. At the bottom, the cable is ---Select-- v and must support his weight as well as provide centripetal acceleration of his body in the upward direction. At this point in his swing, the tension in the cable is the highest and the sandbag is most likely to lift off the floor. Categorize Looking first at the swinging of the actor from the initial point to the lowest point, we model the actor and the Earth as an isolated system. We ignore air resistance, so there are no ---Select--- v forces acting. You might initially be tempted to model the system as nonisolated because of the interaction of the system with the cable, which is in the environment. The force applied to the actor by the cable, however, is always perpendicular to each element of the displacement of the actor and hence does no work. Therefore, in terms of energy transfers across the boundary, the system is isolated. Analyze We first find the actor's speed as he arrives at the floor as a function of the initial angle e and the radius R of the circular path through which he swings. From the isolated system model, make the appropriate reduction of the fully expanded conservation of energy equation for the ---Select--- v system: AK + AU, -0 Let y, be the initial height of the actor above the floor and v,, be his speed at the instant before he lands. (Notice that K, -0 because the actor starts from rest and that U,- O because we define the configuration of the actor at the floor as having a gravitational potential energy of zero. Use the following as necessary: mactor Ve 9, R, and y. Do not substitute numerical values; use variables only.) -)-(-- (1) From the geometry in figure (a), notice that y, - 0, so y,- R - R cos(0) - R(1 - cos(0)). Use this relationship in Equation (1) and solve for v. (Use the following as necessary: g, mactor and R. Do not substitute numerical values; use variables only.) (2) v -
Categorize Next, focus on the instant the actor is at the lowest point. Because the tension in the cable is transferred as a force applied to the sandbag, we model the actor at this instant as a particle ---Select---
Because the actor moves along a circular arc, he experiences at the bottom of the swing a centripetal acceleration of directed upward.
Analyze Apply Newton's second law from the particle under a net force model to the actor at the bottom of his path, using the free-body diagram in figure (b) as a guide, and recognizing the acceleration as centripetal. (Use the
following as necessary: R, g, and v, Do not substitute numerical values; use variables only.)
v?
SF,-T- mactor9 - mactor
mactor
(3) T-
Categorize Finally, notice that the sandbag lifts off the floor when the upward force exerted on it by the cable ---Select--- v the gravitational force acting on it; the normal force from the floor is zero when that happens. We do not,
however, want the sandbag to lift off the floor. The sandbag must remain at rest, so we model it as a particle in equilibrium.
Analyze A force T of the magnitude given by Equation (3) is transmitted by the cable to the sandbag. If the sandbag remains at rest but is just ready to be lifted off the floor if any more force were applied by the cable, the normal
force on it becomes zero and the particle in equilibrium model tells us that T? v mpagg as in figure (c).
Substitute this condition and Equation (2) into Equation (3):
2gR(1 - cos(0))
mpagg - mactor9g + mactor-
Solve for cos(0) and substitute the given parameters, then solve for (in degrees) (Due to the nature of this problem, do not use rounded intermediate values in your calculations-including answers submitted in WebAssign.):
3mactor- moag.
2mactor
1.
cos(e) -
Finalize Here we had to combine several analysis models from different areas of our study. Notice that the length R of the cable from the actor's harness to the leftmost pulley did not appear in the final algebraic equation for cos(0).
Therefore, the final answer is independent of which of the following?
O mactor
OR
O mpag
EXERCISE
The director and his staff forget it is the body-double stuntman who is flying, not the actor. The stuntman's mass is 14 kg more than the actor. At the last second, you are asked to calculate how much extra mass, AM (in kg), to add
to the sandbag in order to maintain the same maximum angle
(Due to the nature of this problem, do not use rounded intermediate values in your calculations-including answers submitted in WebAssign.)
Hint
kg
Need Help? Read It
Transcribed Image Text:Categorize Next, focus on the instant the actor is at the lowest point. Because the tension in the cable is transferred as a force applied to the sandbag, we model the actor at this instant as a particle ---Select--- Because the actor moves along a circular arc, he experiences at the bottom of the swing a centripetal acceleration of directed upward. Analyze Apply Newton's second law from the particle under a net force model to the actor at the bottom of his path, using the free-body diagram in figure (b) as a guide, and recognizing the acceleration as centripetal. (Use the following as necessary: R, g, and v, Do not substitute numerical values; use variables only.) v? SF,-T- mactor9 - mactor mactor (3) T- Categorize Finally, notice that the sandbag lifts off the floor when the upward force exerted on it by the cable ---Select--- v the gravitational force acting on it; the normal force from the floor is zero when that happens. We do not, however, want the sandbag to lift off the floor. The sandbag must remain at rest, so we model it as a particle in equilibrium. Analyze A force T of the magnitude given by Equation (3) is transmitted by the cable to the sandbag. If the sandbag remains at rest but is just ready to be lifted off the floor if any more force were applied by the cable, the normal force on it becomes zero and the particle in equilibrium model tells us that T? v mpagg as in figure (c). Substitute this condition and Equation (2) into Equation (3): 2gR(1 - cos(0)) mpagg - mactor9g + mactor- Solve for cos(0) and substitute the given parameters, then solve for (in degrees) (Due to the nature of this problem, do not use rounded intermediate values in your calculations-including answers submitted in WebAssign.): 3mactor- moag. 2mactor 1. cos(e) - Finalize Here we had to combine several analysis models from different areas of our study. Notice that the length R of the cable from the actor's harness to the leftmost pulley did not appear in the final algebraic equation for cos(0). Therefore, the final answer is independent of which of the following? O mactor OR O mpag EXERCISE The director and his staff forget it is the body-double stuntman who is flying, not the actor. The stuntman's mass is 14 kg more than the actor. At the last second, you are asked to calculate how much extra mass, AM (in kg), to add to the sandbag in order to maintain the same maximum angle (Due to the nature of this problem, do not use rounded intermediate values in your calculations-including answers submitted in WebAssign.) Hint kg Need Help? Read It
Expert Solution
trending now

Trending now

This is a popular solution!

steps

Step by step

Solved in 5 steps with 1 images

Blurred answer
Knowledge Booster
Moments
Learn more about
Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, civil-engineering and related others by exploring similar questions and additional content below.
Similar questions
  • SEE MORE QUESTIONS
Recommended textbooks for you
Structural Analysis
Structural Analysis
Civil Engineering
ISBN:
9781337630931
Author:
KASSIMALI, Aslam.
Publisher:
Cengage,
Structural Analysis (10th Edition)
Structural Analysis (10th Edition)
Civil Engineering
ISBN:
9780134610672
Author:
Russell C. Hibbeler
Publisher:
PEARSON
Principles of Foundation Engineering (MindTap Cou…
Principles of Foundation Engineering (MindTap Cou…
Civil Engineering
ISBN:
9781337705028
Author:
Braja M. Das, Nagaratnam Sivakugan
Publisher:
Cengage Learning
Fundamentals of Structural Analysis
Fundamentals of Structural Analysis
Civil Engineering
ISBN:
9780073398006
Author:
Kenneth M. Leet Emeritus, Chia-Ming Uang, Joel Lanning
Publisher:
McGraw-Hill Education
Sustainable Energy
Sustainable Energy
Civil Engineering
ISBN:
9781337551663
Author:
DUNLAP, Richard A.
Publisher:
Cengage,
Traffic and Highway Engineering
Traffic and Highway Engineering
Civil Engineering
ISBN:
9781305156241
Author:
Garber, Nicholas J.
Publisher:
Cengage Learning