When you touch<span> a doorknob (or something else made of metal), which has a positive charge with few electrons.</span>
        
                    
             
        
        
        
Work = Force times Distance
W = Fd
Given W = 750J, F = 125N;
750 = 125d
Solving for d:
d = 750/125
d = 6
The box moved a distance of 6 meters.
        
             
        
        
        
Answer:
225 N
Explanation:
"Below the horizontal" means he's pushing down at an angle.
Draw a free body diagram of the box.  There are three forces: normal force N pushing up, weight force mg pulling down, and the applied force F at an angle θ.
Sum of forces in the y direction:
∑F = ma
N − mg − F sin θ = 0
N = F sin θ + mg
Plug in values:
N = (50 N) (sin 30°) + (20.0 kg) (10 m/s²)
N = 225 N
 
        
             
        
        
        
Answer:
 λ = a 
Explanation:
This is a diffraction exercise that is described by the expression
           a sin θ = m λ
          sin θ  = m λ/ a
the first zero of the diffraction occurs for m = 1
         sin θ  = λ / a
  
angles are generally very small and are measured in radians
          sin θ  = θ  = y / x
we substitute
           
the width of the central maximum is twice the distance to zero
          w = 2y
in the exercise indicate that this width is equal to twice the distance to the screen (2x)
           W = 2x
            2y = 2x
we substitute
           1 = λ/ a
           λ = a 
we see that the width of the slit is equal to the wavelength used.
 
        
             
        
        
        
Static friction and normal force? I would Google to double check if I'm right.