Physics
Physics
5th Edition
ISBN: 9781260486919
Author: GIAMBATTISTA
Publisher: MCG
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Question
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Chapter 8, Problem 115P

(a)

To determine

The angular velocity when the hoop arrives at the bottom.

(a)

Expert Solution
Check Mark

Answer to Problem 115P

The angular velocity when the hoop arrives at the bottom is 6.28rad/s.

Explanation of Solution

Write an expression to calculate the angular velocity when the hoop arrives at the bottom.

ωf=2ωav=2(vavr)=2((Δx/Δt)(C/2π))=4πΔxCΔt (I)

Here, ωf is the angular velocity when the hoop arrives at the bottom, ωav is the average velocity, vav is the average velocity, r is the radius, Δx is the displacement, Δt is the time and C is the circumference.

Conclusion:

Substitute 10.0m for Δx, 2.00m for C and 10.0s for Δt in equation (I) to find ωf.

ωf=4π(10.0m)(2.00m)(10.0s)=4π(10.0m)(20.0ms)=6.28rad/s

Thus, the angular velocity when the hoop arrives at the bottom is 6.28rad/s.

(b)

To determine

The angular momentum of the hoop at the bottom.

(b)

Expert Solution
Check Mark

Answer to Problem 115P

The angular momentum of the hoop at the bottom is 0.955kgm2/s.

Explanation of Solution

Refer figure 1.

Write an expression for the angular momentum of the hoop at the bottom.

L=Iω=(mr2)ω=m(C2π)2ω (II)

Here, L is the angular momentum of the hoop at the bottom, I is the moment of inertia, m is the mass and ω is the angular velocity.

Conclusion:

Substitute 1.50kg for m, 2.00m for r and 2πrad/s for ω in equation (II) to find τmotor.

L=(1.50kg)(2.00m2π)2(2πrad/s)=(1.50kg)(4.00m24π2)(2πrad/s)=0.955kgm2/s

Thus, the angular momentum of the hoop at the bottom is 0.955kgm2/s.

(c)

To determine

The forces applied the net torque to change the hoop’s angular momentum.

(c)

Expert Solution
Check Mark

Answer to Problem 115P

The forces applied the net torque to change the hoop’s angular momentum is the friction.

Explanation of Solution

The gravitational force is acting at the geometric centre of the hoop. To have a torque to create a change in momentum, the force should act at a distance from the axis of rotation through the geometric centre. Thus, the gravitational force cannot produce a change in momentum.

The force of static friction acts at the rim of the hoop. The force of friction acts perpendicularly to the line between the axis of the hoop and the point of contact between the rim of the hoop and the inclined plane. This can produce torque and hence change in angular momentum. Thus, force of friction causes the net torque about the hoop’s axis.

(d)

To determine

Magnitude of the force that creates the torque.

(d)

Expert Solution
Check Mark

Answer to Problem 115P

Magnitude of the force that creates the torque is 0.300N.

Explanation of Solution

Write an expression for the magnitude of the force that creates the torque.

f=τr=(ΔL/Δt)(C/2π)=2πΔLCΔt (III)

Here, f is the force, τ is the torque and ΔL is the change in angular momentum.

Conclusion:

Substitute 0.955kgm2/s for ΔL, 2.00m for C and 10.0s for Δt in equation (III) to find f.

f=2π(0.955kgm2/s)(2.00m)(10.0s)=2π(0.955kgm2/s)20.0ms=0.300N

Thus, the magnitude of the force that creates the torque is 0.300N.

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Chapter 8 Solutions

Physics

Ch. 8.4 - Prob. 8.8PPCh. 8.4 - Prob. 8.9PPCh. 8.5 - Prob. 8.10PPCh. 8.6 - Prob. 8.11PPCh. 8.7 - Prob. 8.12PPCh. 8.7 - Prob. 8.7CPCh. 8.7 - Prob. 8.13PPCh. 8.8 - Prob. 8.8CPCh. 8.8 - Prob. 8.14PPCh. 8.8 - Prob. 8.15PPCh. 8 - Prob. 1CQCh. 8 - Prob. 2CQCh. 8 - Prob. 3CQCh. 8 - Prob. 4CQCh. 8 - Prob. 5CQCh. 8 - Prob. 6CQCh. 8 - Prob. 7CQCh. 8 - Prob. 8CQCh. 8 - Prob. 9CQCh. 8 - Prob. 10CQCh. 8 - Prob. 11CQCh. 8 - Prob. 12CQCh. 8 - Prob. 13CQCh. 8 - Prob. 14CQCh. 8 - Prob. 15CQCh. 8 - Prob. 16CQCh. 8 - Prob. 17CQCh. 8 - Prob. 18CQCh. 8 - Prob. 19CQCh. 8 - Prob. 20CQCh. 8 - Prob. 21CQCh. 8 - Prob. 1MCQCh. 8 - Prob. 2MCQCh. 8 - Prob. 3MCQCh. 8 - Prob. 4MCQCh. 8 - Prob. 5MCQCh. 8 - Prob. 6MCQCh. 8 - Prob. 7MCQCh. 8 - Prob. 9MCQCh. 8 - Prob. 10MCQCh. 8 - Prob. 1PCh. 8 - Prob. 2PCh. 8 - Prob. 3PCh. 8 - Prob. 4PCh. 8 - Prob. 5PCh. 8 - Prob. 6PCh. 8 - Prob. 7PCh. 8 - Prob. 8PCh. 8 - Prob. 9PCh. 8 - Prob. 10PCh. 8 - Prob. 11PCh. 8 - Prob. 12PCh. 8 - 13. The pull cord of a lawnmower engine is wound...Ch. 8 - Prob. 14PCh. 8 - Prob. 15PCh. 8 - Prob. 16PCh. 8 - Prob. 17PCh. 8 - Prob. 18PCh. 8 - Prob. 19PCh. 8 - Prob. 20PCh. 8 - Prob. 21PCh. 8 - Prob. 22PCh. 8 - Prob. 23PCh. 8 - Prob. 24PCh. 8 - Prob. 25PCh. 8 - Prob. 26PCh. 8 - Prob. 27PCh. 8 - Prob. 28PCh. 8 - Prob. 29PCh. 8 - Prob. 30PCh. 8 - Prob. 31PCh. 8 - 32. A sculpture is 4.00 m tall and has its center...Ch. 8 - Prob. 33PCh. 8 - Prob. 34PCh. 8 - Prob. 35PCh. 8 - Prob. 36PCh. 8 - Prob. 37PCh. 8 - Prob. 38PCh. 8 - Prob. 39PCh. 8 - Prob. 40PCh. 8 - Prob. 41PCh. 8 - 42. A man is doing push-ups. He has a mass of 68...Ch. 8 - Prob. 43PCh. 8 - Prob. 44PCh. 8 - Prob. 45PCh. 8 - Prob. 46PCh. 8 - Prob. 47PCh. 8 - Prob. 48PCh. 8 - Prob. 49PCh. 8 - Prob. 50PCh. 8 - Prob. 51PCh. 8 - Prob. 52PCh. 8 - Prob. 53PCh. 8 - Prob. 54PCh. 8 - Prob. 55PCh. 8 - Prob. 56PCh. 8 - Prob. 57PCh. 8 - Prob. 58PCh. 8 - Prob. 59PCh. 8 - Prob. 60PCh. 8 - Prob. 61PCh. 8 - Prob. 64PCh. 8 - Prob. 62PCh. 8 - Prob. 63PCh. 8 - Prob. 65PCh. 8 - Prob. 67PCh. 8 - Prob. 66PCh. 8 - Prob. 69PCh. 8 - Prob. 68PCh. 8 - Prob. 70PCh. 8 - Prob. 71PCh. 8 - Prob. 72PCh. 8 - Prob. 73PCh. 8 - Prob. 74PCh. 8 - Prob. 75PCh. 8 - Prob. 76PCh. 8 - Prob. 77PCh. 8 - Prob. 78PCh. 8 - Prob. 79PCh. 8 - Prob. 80PCh. 8 - Prob. 81PCh. 8 - Prob. 82PCh. 8 - Prob. 83PCh. 8 - Prob. 84PCh. 8 - Problems 85 and 86. A solid cylindrical disk is to...Ch. 8 - Prob. 86PCh. 8 - Prob. 87PCh. 8 - Prob. 88PCh. 8 - Prob. 89PCh. 8 - Prob. 90PCh. 8 - Prob. 91PCh. 8 - Prob. 92PCh. 8 - Prob. 93PCh. 8 - Prob. 94PCh. 8 - Prob. 95PCh. 8 - Prob. 96PCh. 8 - Prob. 97PCh. 8 - Prob. 98PCh. 8 - Prob. 99PCh. 8 - Prob. 100PCh. 8 - Prob. 101PCh. 8 - Prob. 102PCh. 8 - Prob. 103PCh. 8 - Prob. 104PCh. 8 - Prob. 105PCh. 8 - Prob. 106PCh. 8 - Prob. 107PCh. 8 - Prob. 108PCh. 8 - Prob. 109PCh. 8 - Prob. 110PCh. 8 - Prob. 111PCh. 8 - Prob. 112PCh. 8 - Prob. 113PCh. 8 - Prob. 114PCh. 8 - Prob. 115PCh. 8 - 116. A large clock has a second hand with a mass...Ch. 8 - 117. A planet moves around the Sun in an...Ch. 8 - 118. A 68 kg woman stands straight with both feet...Ch. 8 - Prob. 118PCh. 8 - Prob. 120PCh. 8 - Prob. 121PCh. 8 - Prob. 122PCh. 8 - Prob. 123PCh. 8 - Prob. 125PCh. 8 - Prob. 124PCh. 8 - Prob. 126PCh. 8 - Prob. 127PCh. 8 - Prob. 128PCh. 8 - Prob. 129PCh. 8 - Prob. 130PCh. 8 - Prob. 131PCh. 8 - Prob. 132PCh. 8 - Prob. 133P
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