Angular Velocity & Angular Acceleration

[ladolce]

Homework Statement

A person is riding a bicycle, and its wheels have an angular velocity of +19.5 rad/s. Then, the brakes are applied and the bike is brought to a uniform stop. During braking, the angular displacement of each wheel is +11.5 revolutions.

(a) How much time does it take for the bike to come to rest?

(b) What is the angular acceleration of each wheel?

Homework Equations

avg ang. v=ang. x/t

avg ang. a=change in ang. v / t

The Attempt at a Solution

I plugged in and got...

delta theta=11.5 x 2pi=72.26 radians

and

72.26rad/(t) = 19.5

and so t=3.7 or 3.706 or 3.71 and all those are wrong... I don't know what i did wrong.

 

[Dick]

You are treating this as problem with uniform angular velocity. Clearly that's not true since the bike is slowing down. You need the analog of x(t)=x0+v0*t+(1/2)*a*t^2. Remember linear motion?

 

[ladolce]

thanks i got the problem right after i typed it though =)