# How long will it take to come to rest?

## Homework Statement

A steam engine is running at 200 RPM whe nits steam is shut off. The friction of its various parts produces torques that combine to decelerate the machine at 5.0 rad/s^2. How long will it take to come to rest?

## The Attempt at a Solution

hage567
Homework Helper
You are using the right equation. Note that the angular acceleration is negative, since the steam engine is coming to rest.

THanks but how do I finish it??

hage567
Homework Helper
Solve for t. Are you having trouble with the algebra?

0 rad/s / 25.94t = 0 and that is not right

hage567
Homework Helper
0 rad/s / 25.94t = 0 and that is not right

No, that won't work.

The equation initially is

ωf = ωi + αt

So you have come to the point where you have

0 = 20.94 - 5t

You want to get t on its own on one side of the equation. So the first step is to subtract 20.94 from both sides of the equation (whatever you do to one side you must also do it to the other side). When you do that, what do you get?

THank you I got the answer now. I forgot that the 20.94 needs to go on the other side of the = in order to get t alone. THanks again

hage567
Homework Helper
You're welcome.