iGCSE Physics (0625) 1.2 Motion-Exam Style Questions- New Syllabus
▶️ Answer/Explanation
Detailed solution:
The given figure represents a speed-time graph of a motorcyclist’s journey.
When the motorcyclist is stationary at traffic lights, their speed must be exactly $0$.
On a speed-time graph, a speed of $0$ is represented by a horizontal line that lies entirely on the time axis.
Analyzing the graph, section A shows constant positive speed, and section B represents deceleration.
Section C represents a period where the speed is strictly equal to $0$.
Therefore, section C represents the time when the motorcyclist is entirely stationary.
▶️ Answer/Explanation
Detailed solution:
In a speed–time graph, the gradient represents the acceleration $a$. A straight line indicates constant acceleration, while a curved line indicates changing acceleration.
Section $P$ is a horizontal line where $a = 0$, and section $S$ is a vertical line indicating an instantaneous stop (infinite deceleration), neither of which represents a gradual “change” in acceleration.
Sections $Q$ and $R$ are curved, meaning the gradient is constantly varying as the car speeds up and slows down.
Specifically, in $Q$, the gradient increases then decreases, and in $R$, the negative gradient becomes steeper.
Therefore, only sections $Q$ and $R$ show an acceleration that is changing over time.
▶️ Answer/Explanation
Detailed solution:
When an object falls near the Earth’s surface and air resistance is ignored, it is in a state of free fall.
The only force acting on the ball is its weight, resulting in a constant acceleration due to gravity, $g \approx 9.8 \text{ m/s}^2$.
Since the acceleration is constant and in the direction of motion, the speed of the ball increases at a steady rate.
Option B and C are incorrect because the speed is changing, not remaining constant or decreasing.
Option D is incorrect because the gravitational field strength is uniform, so the acceleration does not increase.
Thus, the ball falls with a constant acceleration, making option A the correct description.