Answer:
B. 24.2 m/s
Explanation:
Given;
mass of the roller coaster, m = 450 kg
height of the roller coaster, h = 30 m
The maximum potential energy of the roller coaster  due to its height is given by;



Therefore, the maximum speed of the roller coaster is 24.2 m/s.
 
        
             
        
        
        
Answer:
The efficiency of Carnot's heat engine is 26.8 %. 
Explanation:
Temperature of hot reservoir, TH = 100 degree C = 373 K
temperature of cold reservoir, Tc = 0 degree C = 273 K
The efficiency of Carnot's heat engine is 
 
 
The efficiency of Carnot's heat engine is 26.8 %.