What is the oxidant?
In one type of fuel cell, the following oxidation-reduction reactions are taking place:
2 H2 + O2 ? 2 H2O
A) H2
B) O2
C) H2O
D) all of the above
E) none of the above
Answer: B
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Pour two liters of water at 40°C into one liter of water at 20°C and the final temperature of the two becomes
A) less than 30°C. B) at or about 30°C. C) more than 30°C.
Two experiments are performed. In (A), an 18.0-N force pushes horizontally on a 2.00-kg block that then pushes on a 4.00-kg block. In (B), an 18.0-N force pushes on a 4.00-kg block that then pushes on a 2.00-kg block. Which statement is correct?
A. The acceleration is 3.00 m/s2 in both (A) and (B). B. The acceleration is 4.50 m/s2 in both (A) and (B). C. The acceleration is 6.00 m/s2 in both (A) and (B). D. The acceleration is 9.00 m/s2 in both (A) and (B). E. The 2.00-kg block has a 9.00 m/s2 acceleration. The 4.00-kg block has a 4.50 m/s2 acceleration.
The cause of electrical shock is predominantly
A) excess current. B) excess voltage. C) reduced resistance. D) none of the above
A 274-N uniform ladder, 11.0 m long, rests against a smooth vertical wall. The coefficient of static friction between ladder and floor is 0.400 . What minimum angle can the ladder make with the floor before it slips?
a. 84.3° b. 68.2° c. 21.8° d. 51.3° e. 11.3°