ASTR 101 — Homework Demo Walkthrough
What Good Work Looks Like
This walkthrough shows you what a complete homework submission and grade memo look like. Use it as a model for your own work.
Sample Problem
Problem: The Sun is about 150 million km from Earth. Light travels at 300,000 km/s. How long does it take sunlight to reach Earth? Express your answer in minutes.
Stage 1: Solution (Monday Submission)
What a 5/5 Solution Looks Like
Given:
- Distance from Sun to Earth: \(d = 150 \times 10^6\) km
- Speed of light: \(c = 3 \times 10^5\) km/s
Find: Time for light to travel from Sun to Earth, in minutes
Solution:
Using \(\text{time} = \frac{\text{distance}}{\text{speed}}\):
\[t = \frac{d}{c} = \frac{150 \times 10^6 \text{ km}}{3 \times 10^5 \text{ km/s}} = 500 \text{ s}\]
Converting to minutes:
\[t = 500 \text{ s} \times \frac{1 \text{ min}}{60 \text{ s}} = 8.3 \text{ min}\]
Answer: Light takes about 8.3 minutes to travel from the Sun to Earth.
Sanity check: This is close to the “8 minutes” you often hear quoted — makes sense!
What a 2/5 Solution Looks Like
\(150000000 / 300000 = 500\)
Answer: 500
Why this is a 2:
- No units shown
- No setup explaining what’s being calculated
- Didn’t convert to minutes (problem asked for minutes)
- No sanity check or interpretation
Stage 2: Grade Memo (Wednesday Submission)
If You Got It Right
| Problem | Score | Why this score? |
|---|---|---|
| 1 | 5 | Showed all steps, units consistent, converted to minutes, answer matches expected ~8 min |
What was confusing? Nothing major — I had to double-check the unit conversion from seconds to minutes.
What would help? I’ll keep practicing scientific notation; I almost made an error with the powers of 10.
Collaboration: No
AI Tools: No
If You Made an Error
Let’s say you forgot to convert to minutes and wrote “500 seconds” as your final answer.
| Problem | Score | Why this score? |
|---|---|---|
| 1 | 4 | Method correct, units tracked, but didn’t convert to minutes as asked |
What was confusing? I didn’t read carefully — missed that it asked for minutes, not seconds.
What would help? Before finishing, I’ll re-read what the problem actually asks for. Circle the units in the question.
Collaboration: No
AI Tools: No
If You Struggled
Let’s say you weren’t sure how to set it up and guessed.
| Problem | Score | Why this score? |
|---|---|---|
| 1 | 2 | Attempted but divided wrong quantities; didn’t track units |
What was confusing? I wasn’t sure whether to multiply or divide. I guessed divide but I don’t really understand why.
What would help? Review the “distance = speed × time” relationship in the reading. Maybe try office hours to work through another example.
Collaboration: Talked to roommate briefly but still confused
AI Tools: No
Key Takeaways
- Show your work — setup, reasoning, units, labeled answer
- Be honest in self-grading — guessing correctly isn’t a 5
- Reflection matters — identifying what confused you is valuable
- Disclosure is required — even if it’s just “none”
The goal isn’t perfection. It’s visible reasoning + honest self-assessment.