UNIVERSITY PHYSICS （20 MARKS）

DAMON

2013-10-21 6:00 am

In a charming 19th-century hotel, an old-style elevator is connected to a counterweight by a cable that passes over a rotating disk 2.50m m in diameter (the figure (Figure 1) ). 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.

Q1 At how many rpm must the disk turn to raise the elevator at 30.0cm/s cm/s ?

Q2 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

Q3 Through what angle (in radians ) has the disk turned when it has raised the elevator 2.95m m between floors?

Q4 Through what angle (in degrees ) has the disk turned when it has raised the elevator 2.95m m between floors?

回答 (1)

天同

2013-10-21 7:43 am

✔ 最佳答案

1. In 1 minute, the elevator rises = 30 x 60 cm = 1800 cm = 18 m
Hence, rotational speed of disk
= 18/(pi.2.5) rpm = 2.292 rpm

2. Angular acceleration = (g/8)/(2.5/2) rad/s^2 = 1 rad/s^2
where g is taken to be 10 m/s^2

3. Angle turned by the disk
= 2.95/(2.5/2) rad. = 2.36 radians

4. Angle turned in degrees
= 2.36 x (180/pi) degrees = 135.2 degrees

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