The Essence of Motion Graphs
When a particle moves, its position, velocity, and acceleration are intimately connected through the language of calculus. Graphs are the visual storytelling of these mathematical relationships. In this problem, we are given a simple yet powerful constraint: the particle moves with constant acceleration. Let's decode what this means for each of its motion graphs.
Acceleration
The Foundation
The problem states that the acceleration a is constant. This means that as time t ticks forward, the value of acceleration does not change.
Mathematically, we write this as:
a(t)=constant
Graphically, a constant value over time is represented by a horizontal straight line. If we assume the acceleration is positive, this line will be parallel to the time axis and above it. This is our first crucial clue.
Velocity
The Linear Climb
Acceleration is defined as the rate of change of velocity.
a=dtdv​
To find the velocity, we integrate the constant acceleration with respect to time:
v(t)=∫adt=at+u
where
u is the initial velocity.
This equation, v(t)=at+u, is a linear equation in the form y=mx+c. The slope of this line is the acceleration a, which is constant and positive. Therefore, the velocity-time graph must be a straight line with a positive slope.
Position
The Parabolic Arc
Finally, let's determine the position. Velocity is the rate of change of position.
v=dtdx​
To find the position, we integrate the linear velocity function:
x(t)=∫vdt=∫(at+u)dt
x(t)=21​at2+ut+x0​
where
x0​ is the initial position.
This is a quadratic equation in terms of time t. In geometry, a quadratic equation represents a parabola. Since the coefficient of t2 (which is 21​a) is positive, this parabola opens upwards.
Bringing It All Together
We have deduced the shapes of all three graphs:
1. Acceleration-time: A horizontal straight line.
2. Velocity-time: A straight line with a positive slope.
3. Position-time: An upward-opening parabola.
Looking at the given options, only Option (b) perfectly matches all three of these deduced shapes. The beauty of kinematics lies in this perfect synchronization between calculus and geometry!