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A disk, initially rotating at 120 rads, is slowed down with a constant angular acceleration of magnitude 120 rads2.

(a) How much time does the disk take to stop?

(b) Through what angle does the disk rotate during that time?

Short Answer

Expert verified
  1. The time required for a disk to come to rest,t=30.0 s
  2. The angular displacement of the disk while it comes to rest,θ=1.8×103rad

Step by step solution

01

Determine the given quantities

The initial angular velocity of the disk,Ӭ0=120 rads

The angular acceleration of the disk,α=−4.0 rads2

02

Determine the concept of kinematic equations

Use the kinematic equation for constant angular acceleration to solve for time and angular displacement.

Ó¬=Ó¬0+α³Ù

θ=Ó¬t−12α³Ù2

03

(a) Calculate the time required by the disk to take stop.

Kinematic equation for angular motion is:

Ó¬=Ó¬0+α³Ùt=Ó¬-Ó¬0α

Substitute the values and solve further as:

t=0−120−4.0=30.0s

The time required for a disk to come to rest, t=30.0 s.

04

(b) Calculate the rotation angle of disk

Consider the formula for the rotation angle as:

θ=Ó¬t−12α³Ù2=0×30.0−12×(−4.0)×30.02=1.8×103 r²¹»å

The angular displacement of the disk while it comes to rest,θ=1.8×103rad.

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