E=F*d/2 = M*g*d/2 = 25kg * 9.8 N/kg *0.65m / 2 = 79.625J
        
                    
             
        
        
        
Answer:
Hello your question is incomplete hence I will give you a general answer on how A van de Graaff generator works 
answer : 
If the electrons falls through a PD of 150mV the electron will gain energy of   150MeV
Explanation:
when a Van de Graff generator is used to accelerate an electron through a PD ( potential difference ) of any value the particle ( electron )  the electron will gain energy  ( eV )  which is is equivalent in value of the PD it accelerated through 
hence if the electrons falls through a PD of 150mV the electron will gain energy of   150MeV
 
        
             
        
        
        
They live half their lives in water and most of their life on land
        
             
        
        
        
Answer:
2. mechanical weathering can produce smaller pieces of rock that have more surface area for chemical weathering to work Explanation:
Mechanical weathering involves activities of living organisms or some geological processes. The bigger rocks are usually reduced to smaller rocks and further reduction might be limited or not posibble mechanically. This reduced rocks now increases the surface area available for chemical weathering; which further reduces the sizes of the rocks below the size range of mechanical weathering. one will recall that the rate of chemical reaction increases with exposed surface area.