Rotational Kinematics HELP!?(adsbygoogle = window.adsbygoogle || []).push({});

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.

1. The problem statement, all variables and given/known data

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

2. Relevant equations

newtonian rotatational formulae.

3. The attempt at a solution

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

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# Homework Help: Rotational kinematics - need some help

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