Because gravity has been known to define as a force of attraction between things that have mass.
        
             
        
        
        
Answer:
100 miles North East. 
Explanation:
Please see attached photo for diagram.
In the attached photo, X represents the magnitude of the total displacement of the train.
Thus, we can obtain the value of X by using the pythagoras theory as illustrated below:
X² = 80² + 60²
X² = 6400 + 3600
X² = 10000
Take the square root of both side 
X = √10000
X = 100 miles. 
Therefore, the magnitude of the total displacement of the train is 100 miles North East. 
 
        
             
        
        
        
Answer:
C. Recheck the numbers of each atom on each side of the equation
to make sure the sides are equal.
D. Choose coefficients that will balance the equation
Explanation:
In balancing of chemical equation, the number of atoms on both sides must be equal in adherence to the law of conservation of mass. 
Using the method of inspection, the equation is first observed to know the relationship between the combining atoms and the resulting ones. 
After observing the reaction, put a coefficient that will balance the equation. Then recheck the number of each atom on both side of the equation. One can repeat the process till the equation is balanced. 
 
        
             
        
        
        
Answer:
 When studying nanotechnology, scientists must be aware that their ideas may not work out. Their work could be very time consuming and cost a lot of money. Finally, scientists do not yet know all of the effects of nanotechnology on human health.
Hope it helps u:)