Radioactive Decay: The activity of a sample reduces from 7.55 × 109 Bq to 5.11 × 109 Bq in 5.50 months.(a) What is its half life?(b) How many months from the start must one wait for the activity to decrease to 10% of its original value?
What will be an ideal response?
(a) 9.77 months (b) 32.4 months
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The temperature at the Sun's core is about ________.
A. 1,500,000 K B. 150,000 K C. 15,000,000 K D. 15,000 K
Helium fusion is called the triple-alpha process because
a. the helium nucleus is known as an alpha particle. b. it occurs very rapidly. c. it requires a temperature three times greater than that of hydrogen fusion. d. it is the third source of the primary fusion processes. e. each reaction produces three carbon nuclei.
A rectangular wooden block measures 10.0 cm × 4.00 cm × 2.00 cm. When the block is placed in water, it floats horizontally, with its bottom face 1.65 cm below the surface. What is the density of the wood?
A) 0.825 g/cm3 B) 1.21 g/cm3 C) 1.65 g/cm3 D) 0.606 g/cm3 E) 0.350g/cm3
Entropy: A 0.42-kg quantity of ethanol, in the liquid state at its melting point of -114.4°C, is frozen at atmospheric pressure. The heat of fusion of ethanol is 1.04 × 105 J/kg, and its molecular mass is 46.1 g/mol. What is the change in the entropy of the ethanol as it freezes?
A. -280 J/K B. -250 J/K C. -310 J/K D. 250 J/K E. 280 J/K