Constant Acceleration
1. **State the problem:**
We have a particle traveling such that its distance $s$ in metres at time $t$ seconds is given by the equation:
$$s = t^2 - 2t + 5$$
We need to show by differentiation that the acceleration is constant, find its value, calculate the velocity at $t=1$, $t=3$, and $t=4$ seconds, and check by drawing the distance-time graph for $t$ from 0 to 5.
2. **Recall formulas and rules:**
- Velocity $v$ is the first derivative of distance $s$ with respect to time $t$:
$$v = \frac{ds}{dt}$$
- Acceleration $a$ is the derivative of velocity with respect to time, or the second derivative of distance:
$$a = \frac{d^2s}{dt^2}$$
- If acceleration is constant, its value will be a constant number (not dependent on $t$).
3. **Differentiate to find velocity:**
Given:
$$s = t^2 - 2t + 5$$
Differentiate with respect to $t$:
$$v = \frac{ds}{dt} = 2t - 2$$
4. **Differentiate velocity to find acceleration:**
$$a = \frac{dv}{dt} = \frac{d}{dt}(2t - 2) = 2$$
Since $a = 2$ is a constant, acceleration is constant.
5. **Calculate velocity at specific times:**
- At $t=1$:
$$v = 2(1) - 2 = 0$$
- At $t=3$:
$$v = 2(3) - 2 = 6 - 2 = 4$$
- At $t=4$:
$$v = 2(4) - 2 = 8 - 2 = 6$$
6. **Interpretation:**
The velocity increases linearly with time, starting from $v=0$ at $t=1$. The acceleration is constant at 2 m/s².
7. **Graph description:**
The graph of $s = t^2 - 2t + 5$ is a parabola opening upwards, with vertex near $t=1$. It starts at $s=5$ when $t=0$, dips slightly near $t=1$, then rises as $t$ increases to 5.
This confirms the distance-time relation and the constant acceleration.
**Final answers:**
- Acceleration $a = 2$ m/s² (constant)
- Velocity at $t=1$ is 0 m/s
- Velocity at $t=3$ is 4 m/s
- Velocity at $t=4$ is 6 m/s