iGCSE Physics (0625) 1.7.1 Energy-Exam Style Questions- New Syllabus
▶️ Answer/Explanation
Detailed solution:
In a vacuum (no air resistance), all objects fall with the same constant acceleration $g \approx 9.8$ $m/s^{2}$, regardless of mass.
The final velocity $v$ upon hitting the ground is determined by $v = \sqrt{2gh}$, meaning higher drop heights result in higher final speeds.
Average speed for an object starting from rest is $v_{avg} = \frac{0 + v}{2}$, which is directly proportional to $\sqrt{h}$.
Since ball D is dropped from the greatest height ($4.0$ m), it will reach the highest final velocity and thus have the greatest average speed.
Mass does not affect the motion parameters in this scenario as $g$ is independent of the object’s mass.
▶️ Answer/Explanation
Detailed solution:
According to the principle of conservation of energy, the total energy in a system remains constant.
The initial gravitational potential energy ($\Delta E_{p} = 46 \text{ J}$) is transferred as the stone falls.
Part of this energy is used to do work against air resistance ($W = 21 \text{ J}$), which is dissipated as thermal energy.
The remaining energy is converted into the stone’s kinetic energy gain ($\Delta E_{k}$).
Using the equation: $\Delta E_{p} = \Delta E_{k} + W$, we find $\Delta E_{k} = 46 \text{ J} – 21 \text{ J}$.
Therefore, the gain in kinetic energy is $25 \text{ J}$.
▶️ Answer/Explanation
Detailed solution:
In a free-fall scenario, the force of gravity acts on the object, causing it to move through a distance.
Energy transfer via a force is defined as mechanical work, where W=Fd.
As the object descends, the gravitational force does work to convert ΔE p =mgΔh into E k = 2 1 mv 2 .
Options A, B, and C describe transfers via electricity, radiation, or thermal pathways, which do not drive this motion.
Therefore, the transition from the potential store to the kinetic store is achieved through mechanical work.
This aligns with the principle that mechanical working occurs when a force moves an object.