F = ma (force = mass x acceleration)
So the car’s mass affects the amount of force, changing how it would roll down a ramp, I think.
        
                    
             
        
        
        
Answer:
B. 25 feet
Explanation:
In most cities in US, passenger car brakes must stop a car moving at 20 miles per hour at 25 feet. 
Therefore, the correct option is "B" 25 feet
 
        
                    
             
        
        
        
Answer:
Explanation:
Electric field E = 4 x 10⁷ V / m 
Dielectric constant k = 24
capacitance of capacitor
C = kε₀ A / d
d = plate separation 
A =  plate area 
C = .89 x 10⁻⁶
V / d = electric field 
for minimum d , electric field will be maximum
V / d  = 4 x 10⁷
1930 / d = 4 x 10⁷
d = 1930 / 4 x 10⁷
d = 482.5 x 10⁻⁷ m
= 48.25 x 10⁻⁶ m 
C = kε₀ A / d
.89 x 10⁻⁶ = 24 ε₀ A / d
A = .89 x 10⁻⁶  X d /  24 ε₀
A = .89 x 10⁻⁶  X 48.25 x 10⁻⁶  /  24  x 8.85 x 10⁻¹²
= 42.9 / 212.4 
= .2019 m²
 
        
                    
             
        
        
        
Explanation:
Exothermic reaction is defined as the reaction in which release of heat takes place. This also means that in an exothermic reaction, bond energies of reactants is less than the bond energies of products.
Hence, difference between the energies between the reactants and products releases as heat and therefore, enthalpy of the system will decrease.
Whereas in an endothermic reaction, heat is supplied from outside and absorbed by the reactant molecules. Hence, enthalpy of the system increases.
As water acts as a coolent and when fuel rods in a nuclear reactor are immersed in it then heat created by coolent is absorbed by water and then it changes into steam.
Since, absorption of heat occurs in the nuclear reactor. Therefore, it is an endothermic reaction. 
Thus, we can conclude that nuclear reactors use fuel rods to heat water and generate steam. This process is endothermic. 
 
        
                    
             
        
        
        
Answer: A) highly mobile electrons in the valence shell
Explanation: conductivity in metals is a result of the movement of electrically charged particles—the electrons. These free electrons also known as valence electrons are free to move, and as a result they can travel through the lattice that forms the physical structure of a metal. The presence of valence electrons determines a metal's conductivity. However, several other factors can affect the conductivity of a metal such as impurities, temperature, magnetic fields etc.