Probably C...:):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):)
Answer:
The value is 
Explanation:
From the question we are told that
The weight of the horizontal solid disk is
The radius of the horizontal solid disk is
The force applied by the child is
The time considered is 
Generally the mass of the horizontal solid disk is mathematically represented as

=> 
=> 
Generally the moment of inertia of the horizontal solid disk is mathematically represented as

=>
=> 
Generally the net torque experienced by the horizontal solid disk is mathematically represented as

=> 
=> 
=> 
Gnerally from kinematic equation we have that

Here
is the initial angular velocity velocity of the horizontal solid disk which is 
So

=>
Generally the kinetic energy is mathematically represented as

=> 
=> 
Answer:
V = 0.39 m/s
Explanation:
Given that,
Mass of hockey puck, m = 0.2 kg
Mass of goalie = 40 kg
Speed of hockey puck, v = 80 m/s
We need to find the speed with which the goalie slide on the slide. Let V be the speed. Using the conservation of momentum as follows :

So, the required speed is 0.39 m/s.
Rearranging formulas is all about simple algebra rules. Just like when solving for x in an equation, you're just isolating whichever variable you want. I'll work this one out for you and hopefully it'll help, but if you need more explanation, then feel free to comment!
D = ViT + 0.5at² Subtract ViT from both sides
D - ViT = 0.5at² Divide both sides by 0.5t²
I wrote this step out a little more to show how your fraction will cancel
= a I like to flip these around so the single variable is on the right
a = 