The sun is bright and when its cold there is no sun
To solve this problem it is only necessary to apply the kinematic equations of angular motion description, for this purpose we know by definition that,

Where,
Angular Displacement
Angular Acceleration
Angular velocity
Initial angular displacement
For this case we have neither angular velocity nor initial angular displacement, then

Re-arrange for 

Replacing our values,


Therefore the ANgular acceleration of the mass is 
Answer:
Mechanical waves require a medium in order to transport their energy from one location to another.
Sound waves are incapable of traveling through a vacuum. Slinky waves, water waves, stadium waves, and jump rope waves are other examples of mechanical waves; each requires some medium in order to exist.
An example of a balanced force is two cards leaning against each other and not falling over, or two football players blocking each other but neither overpowering the other. An example of an unbalanced force is two cards leaning on each other then falling over, or two football players blocking each other, then one tackles the other.