a) The wheel takes 112.7 s to comes to rest
b) The angular acceleration of the wheel is
c) The wheel takes 33.0 s to complete 13 revolutions
Explanation:
a)
The rotational motion of the wheel is at constant angular acceleration, so we can use the equivalent of the suvat equations for rotational motion. In particular, to find the time the wheel takes to come to a stop, we use the following:
where:
is the angular displacement
is the initial angular speed
is the final angular speed
t is the time
For the wheel in this problem:
And solving for t, we find the time:
b)
We can find the angular acceleration by using the equation:
where here we have:
is the final angular speed
is the initial angular speed
t = 112.7 s is the time
And substituting,
And the negative sign is because the wheel is decelerating.
c)
In order to find the time taken to complete 13 revolutions, we use the following suvat equation:
where:
is the initial angular speed
is the angular displacement
is the angular acceleration
Substituting into the equation:
which has two solutions:
t = 33.0 s
t = 191.8 s
And here we have to take the first solution (33.0 s), because it corresponds to the first time at which the angular displacement of the wheel is equal to 13 revolutions (the second solution is the time at which the angular displacement of the wheel returns to 13 revolutions, after the wheel has came to rest and it started to rotate in the opposite direction).
Learn more about rotational motions:
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