Question

A person is riding a bicycle, and its wheels have an angular velocity of 10.7 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 19.5 revolutions.
(a) How much time does it take for the bike to come to rest?
(b) What is the anguar acceleration (in rad/s2) of each wheel?

Answer 1

Answer:

(a) t = 22.9 s

(b) α= - 0.467 rad/s²

Explanation:

The uniformly accelerated circular movement, is a circular path movement in which the angular acceleration is constant.

We apply the equations of circular motion uniformly accelerated :

ωf ²=  ω₀² + 2*α*θ  Formula (1)

ωf= ω₀ + α*t Formula (2)

Where:

θ : angle that the body has rotated in a given time interval (rad)

α : angular acceleration (rad/s²)

t : time interval (s)

ω₀ : initial angular speed ( rad/s)

ωf : final angular speed ( rad/s)

Data

θ =  19.5 revolutions  : angular displacement of each wheel or angle that the  wheel has rotated in a given time interval

ω₀= 10.7 rad/s :  initial angular speed of the Wheel ( rad/s)

ωf = 0 : final angular speed  of the Whee( rad/s)

Calculating of the angular acceleration (α )

We replace data in the fómula (1),considering that 1 revolution is equal to 2π radians :

ωf ²=  ω₀² + 2*α*θ

(0 )²=  (10.7)² + 2*α*(19.5*2*π )

0= 114.49 + (245.04)*α

-114.49 =  (245.04)*α

α= (-114.49) /(245.04)

α= -114.49 /(245.04)

α= -0.467 rad/s²

Time does it take for the bike to come to rest

We replace data in the formula (2)

ωf = ω₀ + α*t

0 =  10.7 + -0.467*t

-10.7  = - 0.467*t    we multiply by (-1) both sides of the equation :

10.7  = 0.467*t  

t = 10.7 / 0.467

t = 22.9 s