Air pressure pushing in on the balloon decreases as the balloon rises.
        
                    
             
        
        
        
Answer:
All these is caused by the repulsion force.
Explanation:
The electroscope produces a series of electric charges that produce a repulsion force when is putted in contact with a electric charged object.
As the physics law mentions, two different forces are repealed, the electrocospe is charged negatively and the object positively, causing a repulsion force that avoids that both objects touch the other.
 
        
             
        
        
        
Answer:
Explanation:
Given
Horizontal bar rises with 300 mm/s
Let us take the horizontal component of P be 


where  is angle made by horizontal bar with x axis
is angle made by horizontal bar with x axis
Velocity at y=150 mm

thus 
position of


Velocity at this instant


 
        
             
        
        
        
The answer is 3. Internal energy decrease