Answer:
Efficiency is the percent of work put into a machine by the user (input work) that becomes work done by the machine (output work).
Explanation:
It is a measure of how well a machine reduces friction.
 
        
             
        
        
        
The answer is electricity 
        
                    
             
        
        
        
Answer:
From question (a) and (b) the pendulum motion is perpendicular to the force so the normal force will do no work and the tension in the string of the pendulum will not work 
        
And  so
 so 
            
c 
An example will be a where a stone is attached to the end of a string and is made to move in a circular motion while keeping the other end of the string in a fixed position        
d
A dog walking along a surface which has friction, here the frictional force would acting in the direction of the motion and this would do positive work  
Explanation:
 
        
                    
             
        
        
        
Answer:
  v_f = 24.3 m / s
Explanation:
A) In this exercise there is no friction so energy is conserved.
Starting point. On the roof of the building
          Em₀ = K + U = ½ m v₀² + m g y₀
Final point. On the floor
          Em_f = K = ½ m v_f²
          Emo = Em_g
          ½ m v₀² + m g y₀ = ½ m v_f²
         v_f² = v₀² + 2 g y₀
          
let's calculate
         v_f = √(10² + 2 9.8 25)
         v_f = 24.3 m / s