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Answer:
True! First step is to make objective observations. 
 
        
                    
             
        
        
        
Objects should be cooled before their mass is determined on a sensitive balance because it could damage the balance. Also, because it would give you wrong reading of the mass. Hot objects would warm the air around it. A warm air would expand and would produce convection as it rises causing to give the object a mass that is less than the actual. Another reason would be it would cause instability in the readings, the mass would fluctuate every now and then due to the convection currents around the object. It is always recommended to weigh the masses of objects that are in room temperature.
        
             
        
        
        
Answer:
0.8s
Explanation:
Given parameters: 
Height of shelf  = 3m 
Unknown: 
Time it will take to hit the ground  = ? 
Solution: 
To solve this problem, we use the expression below; 
          x  = ut +  gt²
 gt²  
x is the height
u is the initial velocity  = 0m/s 
g is the acceleration due to gravity  = 9.8m/s² 
t is the time taken  = ?
Now insert the parameters and solve for t; 
     3  = (0 x t) +(  x 9.8 x t²)
 x 9.8 x t²)
     3 = 4.9t² 
        t² = 0.6
        t = 0.8s
 
        
             
        
        
        
Answer:
body position 4 is (-1,133, -1.83)
Explanation:
The concept of center of gravity is of great importance since in this all external forces are considered applied, it is defined by
                x_cm = 1 /M   ∑  m_{i}
 m_{i}
                y_cm = 1 /M   ∑ y_{i} mi
Where M is the total mass of the body, mi is the mass of each element
give us the mass and position of this masses
body 1
m1 = 2.00 ka
x1 = 0 me
y1 = 0 me
body 2
m2 = 2.20 kg
x2 = 0m
y2 = 5 m
body 3
m3 = 3.4 kg
x3 = 2.00 m
y3 = 0
body 4
 m4 = 6 kg
    
x4=?
    y4=?
mass center position
x_cm = 0
y_cm = 0
let's apply to the equations of the initial part
X axis
     M = 2.00 + 2.20 + 3.40
     M = 7.6 kg
     0 = 1 / 7.6 (2 0 + 2.2 0 + 3.4 2 + 6 x4)
      x4 = -6.8 / 6
      x4 = -1,133 m
Axis y
     0 = 1 / 7.6 (2 0 + 2.20 5 +3.4 0 + 6 y4)
     y4 = -11/6
     y4 = -1.83 m
body position 4 is (-1,133, -1.83)