Question

1. which of the following materials is used in nuclear reactors to moderate the speed of neutrons for the fission process?

a. uranium rod
b. boron rod
c. graphite rod
d. concrete shield

1. an object of mass 0.1 kg cools from 40° to 34°. calculate the amount of heat released by the object. specific heat capacity of the object is 0.4 j kg⁻¹k⁻¹

a. 5.61 × 10³ j
b. 1.36 × 10³ j
c. 0.24 × 10³ j
d. 9.15 × 10³ j

1. a cyclist travels up a hill from point, x to point, y as illustrated in the diagram below. the major energy transformation from x to y is

diagram: x at bottom, y at top of a hill
a. gravitational potential to kinetic.
b. potential energy.
c. kinetic to gravitational potential.
d. heat to kinetic.

Explanation:

Question 8

• Option A: Uranium rod is a fuel in nuclear reactors, not a moderator.
• Option B: Boron rod is used to control the reaction (absorb neutrons), not moderate.
• Option C: Graphite rod is a common moderator to slow down neutrons for fission.
• Option D: Concrete shield is for radiation protection, not moderation.

Step1: Recall the heat formula

The formula for heat released \( Q \) is \( Q = mc\Delta T \), where \( m \) is mass, \( c \) is specific heat capacity, and \( \Delta T \) is temperature change.

Step2: Identify values

\( m = 0.1 \, \text{kg} \), \( c = 0.4 \, \text{J kg}^{-1}\text{K}^{-1} \), initial temperature \( T_1 = 40^\circ \text{C} \), final temperature \( T_2 = 34^\circ \text{C} \). So \( \Delta T = T_1 - T_2 = 40 - 34 = 6 \, \text{K} \) (change in Celsius is same as Kelvin for temperature difference).

Step3: Calculate \( Q \)

Substitute into formula: \( Q = 0.1 \times 0.4 \times 6 \). First, \( 0.1 \times 0.4 = 0.04 \), then \( 0.04 \times 6 = 0.24 \). So \( Q = 0.24 \times 10^3 \, \text{J} \).

• At point X, the cyclist has kinetic energy (moving). At point Y (higher elevation), the cyclist has more gravitational potential energy. So energy transforms from kinetic to gravitational potential.
• Option A: Opposite of correct transformation.
• Option B: Incomplete (doesn't mention energy source or transformation).
• Option D: Heat to kinetic is not the case here (cyclist's motion to height increase).

Answer:

C. Graphite rod

Question 9