iGCSE Physics (0625) 1.5 Forces-Exam Style Questions- New Syllabus
▶️ Answer/Explanation
Detailed solution:
The car starts from rest and accelerates due to a constant driving force. As speed increases, the resistive forces (drag and friction) also increase because they are proportional to speed. According to $F_{resultant} = F_{driving} – F_{resistive}$, the net force decreases as the resistive force grows. Eventually, the resistive force increases until it equals the driving force, resulting in $F_{resultant} = 0$. At this point, the acceleration $a = \frac{F}{m}$ becomes $0$, and the car reaches a constant maximum speed (terminal velocity).
▶️ Answer/Explanation
Detailed solution:
When a person lies on the bed, their weight exerts a force $F$ that compresses the springs in the mattress.
This compression causes a change in the shape of the springs, resulting in work being done to deform them.
The energy transferred by this work is stored as elastic (strain) energy within the material of the springs.
According to the syllabus, the energy in an elastic store is calculated using $E_{e} = \frac{1}{2}kx^{2}$, where $x$ is the compression.
As the compression $x$ increases from zero, the elastic energy store of the mattress must increase.
Other stores like chemical or kinetic do not increase as the mattress remains stationary and no chemical reaction occurs.
▶️ Answer/Explanation
Detailed solution:
According to the syllabus, forces can cause an object to change its shape or size, such as stretching a spring. Additionally, a resultant force $F$ causes an object of mass $m$ to undergo acceleration $a$, governed by $F = ma$, which changes its speed. However, mass is defined as the quantity of matter in an object; applying a force does not add or remove matter. Therefore, while velocity, size, and shape are all variable under the influence of a force, the mass remains constant.