iGCSE Physics (0625) 1.7.1 Energy-Exam Style Questions- New Syllabus
▶️ Answer/Explanation
Detailed solution:
The kinetic energy of an object is given by the formula $E_{k} = \frac{1}{2}mv^{2}$.
Since the mass $m$ of the car remains constant, the kinetic energy is directly proportional to the square of its speed ($E_{k} \propto v^{2}$).
The initial speed is $v_{1} = 8.0\text{ m/s}$ and the final speed is $v_{2} = 16\text{ m/s}$, meaning the speed has exactly doubled (increased by a factor of $2$).
Because the speed increases by a factor of $2$, the kinetic energy increases by a factor of $2^{2} = 4$.
The new kinetic energy is $4 \times 32\,000\text{ J} = 128\,000\text{ J}$.
Rounding this value to two significant figures, consistent with the given initial speed of $8.0\text{ m/s}$, yields $130\,000\text{ J}$.
▶️ Answer/Explanation
Detailed solution:
The stone’s initial gravitational potential energy is converted into kinetic energy as it falls.
Using the principle of conservation of energy: $mgh = \frac{1}{2}mv^2$, which simplifies to $v = \sqrt{2gh}$.
Substituting the values $g = 9.8\text{ m/s}^2$ and $h = 22\text{ m}$, we get $v = \sqrt{2 \times 9.8 \times 22}$.
Calculation: $v = \sqrt{431.2} \approx 20.76\text{ m/s}$.
Rounding to two significant figures, the speed of the stone is $21\text{ m/s}$.
Therefore, the correct choice is Option B.
▶️ Answer/Explanation
Detailed solution:
Kinetic energy is the energy an object possesses due to its motion, defined by $E_{k} = \frac{1}{2}mv^{2}$.
Wind is the movement of air masses; therefore, the energy resource itself consists of moving matter with velocity $v$.
In contrast, coal stores energy as chemical energy, and nuclear fission involves energy stored within the atomic nucleus.
Solar energy is transferred via electromagnetic radiation (light and infrared waves) rather than being stored as bulk motion.
Since wind is the only resource listed that is inherently defined by the motion of mass, it is the correct choice.
Therefore, Option D accurately identifies the resource that stores kinetic energy.