A uniform, 4.5 kg, square, solid wooden gate 2.0 mm on each side hangs vertically from a frictionless pivot at the center of its upper edge. A 1.2 kg raven flying horizontally at 5.0 m/s flies into this door at its center and bounces back at 1.5 m/s in the opposite direction. What is the angular speed of the gate just after it is struck by the unfortunate raven?

The angular velocity is  

Explanation:

From the question we are told that

   The  mass of wooden gate  is

    The  length of side is  L = 2 m

    The mass of the raven is  

     The initial speed of the raven is

     The final speed of the raven is  

From the law of  conservation of angular momentum we express this question mathematically as

       Total initial angular momentum  of both the Raven and  the Gate =  The Final angular momentum of both the Raven and the Gate  

The initial angular momentum of the Raven is

Note: the length is half because the Raven hit the gate at the mid point

The initial angular momentum of the Gate is  zero

Note: This above is the generally formula for angular momentum of  square objects

  The final angular velocity  of the Raven is  

   The  final angular velocity of the Gate  is  

Substituting this formula

Where is the angular velocity

     Substituting value  

i think the correct answer from the choices listed above is option c. when the kinetic energy of particles in a liquid state decreases

explanation:

we need to know the time interval during which the force acts. impulse of force = momentum change