Angular deceleration of a washing machine spin cycle

[Zoubayr]

Homework Statement

If you lift the lid of a washing machine during the rapid
spin–dry cycle, the cycle stops (for safety), typically after 5.0
revolutions. If the clothes are spinning at 6.0 rev/s initially,
what is their constant angular acceleration during the slowing
motion? How long do they take to come to a stop?

Relevant Equations

w=w_o+αt

6.0 rev - 1 s
1 rev - 1/6
5.0 rev - (1/6) x 5 = (5/6) s = 0.833 s

I do not know how to calculate the angular acceleration

 

[bob012345]

Homework Statement:: If you lift the lid of a washing machine during the rapid
spin–dry cycle, the cycle stops (for safety), typically after 5.0
revolutions. If the clothes are spinning at 6.0 rev/s initially,
what is their constant angular acceleration during the slowing
motion? How long do they take to come to a stop?
Relevant Equations:: w=w_o+αt

6.0 rev - 1 s
1 rev - 1/6
5.0 rev - (1/6) x 5 = (5/6) s = 0.833 s

I do not know how to calculate the angular acceleration

You need a second equation since you are looking to solve two unknowns, $\alpha$ and $t$. They give you a hint by giving you the stopping distance $\theta$.

 

[malawi_glenn]

There is another equation relating angular speeds, angular acceleration and total angle. That equation does not have time in it.

 

[Zoubayr]

There is another equation relating angular speeds, angular acceleration and total angle. That equation does not have time in it.

w^2=(w_0)^2+2αθ
how to know the total angle θ?

 

[bob012345]

w^2=(w_0)^2+2αθ
how to know the total angle θ?

The angle is given. It is 5 revolutions.

 

[Zoubayr]

The angle is given. It is 5 revolutions.

so by using the formula: w^2=(w_0)^2+2αθ with w_0 being 6.0 rev/s, w being zero and θ being 5 we get the answer?

 

[bob012345]

so by using the formula: w^2=(w_0)^2+2αθ with w_0 being 6.0 rev/s, w being zero and θ being 5 we get the answer?

One of the answers. How do you get the time next?

 

[Zoubayr]

One of the answers. How do you get the time next?

using this equation: w=w_o+αt with w_0 being 6.0 rev/s, w being zero and α being the value calculated from the 1st part of the question.

 

[bob012345]

using this equation: w=w_o+αt with w_0 being 6.0 rev/s, w being zero and α being the value calculated from the 1st part of the question.

Note that the acceleration is a negative number from the first part giving the time as a positive number in the second part which is good.

 

[malawi_glenn]

and θ being 5 we get the answer?

What units do we measure angles with in the context of rotational dynamics?