That they sometimes explode?
        
                    
             
        
        
        
Explanation:
The energy stored in coal is directly form the sun which is solar energy. This energy are preserved in carbon atoms and they originate from the life processes of a plant. 
- Plants carry out photosynthesis and produce their energy by this process. 
- Green plants have special adapted structures by which they trap solar energy from the sun and use it to produce their own food. 
- The food is used by plant for nutrition and life activities. 
- In essence the solar energy is converted to chemical energy in plants. 
- To form coal, when plants are rapidly buried their organic matter is preserved from decay by combination with oxygen. 
- More burial preserves the complex molecules that have stored during photosynthesis. 
- The carbon eventually aggregates for coal. 
learn more: 
Coal brainly.com/question/10055728
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v = v₀ + at
v = final speed, v₀ = initial speed, a = acceleration, t = elapsed time
Given values:
v₀ = 0m/s (starts from rest), a = 9.81m/s², t = 3s
Plug in and solve for v:
v = 0 + 9.81(3)
v = 29.4m/s
 
        
             
        
        
        
Solid and liquids are much more denser than gas because their molecules are close to each other and with that the molecules of them can't move that freely unlike the gas molecules. Also, because of being near to each other the molecules of solid and liquids became heavy making them dense.