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In a charming 19th-century hotel, an old-style elevator is connected to a counterweight by a cable that passes over a rotating disk 2.50 m in diameter (Fig. E9.18). The elevator is raised and lowered by turning the disk, and the cable does not slip on the rim of the disk but turns with it.

(a) At how many rpm must the disk turn to raise the elevator at 25.0 cm/s?

(b) To start the elevator moving, it must be accelerated at 1 8 g. What must be the angular acceleration of the disk, in rad/s 2?

(c) Through what angle (in radians and degrees) has the disk turned when it has raised the elevator 3.25 m between floors?

Short Answer

Expert verified

(a) The angular speed of the wheel is 1.91rad.

(b) Thus, the angular acceleration of the wheel is 0.981rads2.

(c) Thus, the angular displacement is 149.76°.

Step by step solution

01

Step:-1explanation

g = acceleration due to gravity=9.81ms2

a = acceleration=18g

d = diameter of the wheel=2.50

r = radius of the wheel=2.502

v = speed of elevator=1.25=25cms

02

Step:-2Concept

here we solve our question first we need to find angular velocity.

We know that the angular velocity formula,

Ó¬=vr

03

Step:-3 calculation

Ӭ=0.251.25rads=0.2×602π

We know that the value ofπ=3.14

=0.2×602×3.14=126.28=1.91rad

The angular speed of the wheel is 1.91rad.

04

(b) Step:-1 explanation

g = acceleration due to gravity=9.81ms2

a = acceleration=18g

d = diameter of the wheel=2.50

r = radius of the wheel=2.502

05

(b) Step:-2Concept

We know that the formula of the angular acceleration,

α=ar

06

(b) Step:-3 Calculation 

We know that value of g=9.81and r=1.25.

Put the value in the expression,then we get

α=18×g1.25α=0.125×9.811.25=1.226251.25=0.981rads2

The angular acceleration of the wheel is 0.981rads2.

07

(c) Step:-1 explanation

r = radius of the wheel=2.502

s = displacement = 3.25

08

(c) Step:-2Concept

We know that θ=sr.

=3.251.25=2.6rad

09

(c) Step:-3 calculation

we know that1rad=3602Ï€.

=2.6×3602π=2.6×362×3.14=2.6×366.25=9362.25=149.760

The angular displacement of the wheel 149.760.

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