Let's call 

 the mass of the glider and 

 the total mass of the seven washers hanging from the string. 
The net force on the system is given by the weight of the hanging washers:

For Newton's second law, this net force is equal to the product between the total mass of the system (which is 

) and the acceleration a:

So, if we equalize the two equations, we get

and from this we can find the acceleration:
 
 
        
        
        
Answer:
True.
Explanation:
If the sum of the external forces on an object is zero, then the sum of the external torques on it  must also be zero.
The net external force and the net external torque acting on the object have to be zero for an object to be in mechanical equilibrium.
Hence, the given statement is true.
 
        
             
        
        
        
Answer:
Only the hydrogen needs to be balanced. There are equal numbers of aluminum and chlorine.
Explanation:
I took the K12 test, listened to some other idiot and got it wrong, so this is the correct one.
Hope this helps!
 
        
                    
             
        
        
        
I believe the answer is #4. u can always ask google if u believe that's the wrong answer :)
        
                    
             
        
        
        
Answer: A The energy and intensity of X-rays can be controlled.|
Explanation: