How Can I Solve These Rotational Kinematics Problems?

[HT3]

Rotational Kinematics HELP!?

I desperately need help with two rotational kinematics problems. I do not know what to do in both cases. If someone could be kind enough to go through a solution for me to see it would be very helpful in understanding the problem. Please try and be detailed in your answer as I really want to understand how it is solved.

Homework Statement

1) A spinning wheel on a fireworks display is initially rotating in a counterclockwise direction. The wheel has an angular acceleration of -4.00rad/s2. Because of this acceleration, the angular velocity of the wheel changes from its initial value to a final value of -25.0rad/s. While this change occurs, the angular displacement of the wheel is zero. Find the time required for the change in the angular velocity to occur.
Answer: 12.5s

2) A fan blade whose angular acceleration is a constant 2.00 rad/s^2 rotates through an angle of 285 radians in 11.0s. How long did it take the blade starting from rest to reach the beginning of the 11.0s interval?
Answer: 7.45s

Homework Equations

Newtonian rotatational formulae.

The Attempt at a Solution

no idea i did the last 20 problems no problems but these 2 are stumping me.

 

[Kurdt]

What have you tried so far. We can't give full solutions here, only guide the student to the correct answer. I suggest you review the following web page.

http://hyperphysics.phy-astr.gsu.edu/HBASE/rotq.html#drot

 

[physixguru]

These hints should be enough:

1).negative acceleration means deceleration.
zero angular displacement means one complete revolution.
counter clockwise is positive direction.

2).2 pi radian = 1 revolution.
calculate the distance traversed in the desired time interval.

 

[JaWiB]

1) A spinning wheel on a fireworks display is initially rotating in a counterclockwise direction. The wheel has an angular acceleration of -4.00rad/s2. Because of this acceleration, the angular velocity of the wheel changes from its initial value to a final value of -25.0rad/s. While this change occurs, the angular displacement of the wheel is zero. Find the time required for the change in the angular velocity to occur.
Answer: 12.5s

I don't see how there's enough information there to answer the question. Specifically, what is the initial angular velocity?