Velocity, acceleration and speed in space
Problem 9.398 · medium
A particle has acceleration \( \displaystyle \mathbf a(t) = \left\langle 0, 0, - \frac{49}{5} \right\rangle \), initial velocity \( \displaystyle \left\langle 0, 2, 2 \right\rangle \) and initial position \( \displaystyle \left\langle 0, -1, -3 \right\rangle \). Find \( \displaystyle \mathbf r(t) \).
- \[ \left[\begin{matrix}\frac{d}{d t} 0\\\frac{d}{d t} 2\\\frac{d}{d t} \left(2 - \frac{49 t}{5}\right)\end{matrix}\right] = \left[\begin{matrix}0\\0\\- \frac{49}{5}\end{matrix}\right] \]Integrating a and using v(0) gives v(t) = <0, 2, 2 - 49*t/5>.✓ Proved
- \[ \left[\begin{matrix}\frac{d}{d t} 0\\\frac{d}{d t} \left(2 t - 1\right)\\\frac{d}{d t} \left(- \frac{49 t^{2}}{10} + 2 t - 3\right)\end{matrix}\right] = \left[\begin{matrix}0\\2\\2 - \frac{49 t}{5}\end{matrix}\right] \]Integrate again and use r(0).✓ Proved
- \[ \left[\begin{matrix}0\\-1\\-3\end{matrix}\right] \]r(0) is the given position.✓ Proved
Answer \( \mathbf r(t) = \left\langle 0, 2 t - 1, - \frac{49 t^{2}}{10} + 2 t - 3 \right\rangle \)
✓ Nihil obstat Every line of this solution was proved by the computer algebra system SymPy. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation.
The full receipt
| Line | Status | Checked by | Detail |
|---|---|---|---|
| 1 | ✓ Proved | sympy 1.14.0 | simplify(lhs - rhs) reduced to 0 |
| 2 | ✓ Proved | sympy 1.14.0 | simplify(lhs - rhs) reduced to 0 |
| 3 | ✓ Proved | sympy 1.14.0 | simplify(lhs - rhs) reduced to 0 |
| answer, a second way | ✓ Checked independently | sympy 1.14.0 + mpmath 1.3.0 | the motion integrated numerically from the initial conditions, compared at t = 1.5 |
Reviewers
gpt-oss:20b: passqwen3.6:27b-mlx: pass
Every verdict on record (4)
qwen3.6:27b-mlx: pass 2026-10-08gpt-oss:20b: pass 2026-10-08gpt-oss:20b: pass 2026-10-08qwen3.6:27b-mlx: pass 2026-10-08 — The solution correctly integrates the acceleration to find velocity and then position, applying the initial conditions accurately. The final result matches the stated answer.
Proved: SymPy reduced the difference between the two sides to zero. Checked independently: a separate
method, named above, confirmed it. Checked numerically: the two sides agree at every sampled point, which is evidence,
not proof. Reviewed: a model or a person read it; that is all a sentence can have. Solution by
generator:structured/motion_in_space, checked 2026-10-08 with SymPy 1.14.0.