A satellite is currently in a circular orbit with radius 32,714 km about the center of the earth.
GMAT Two Part Analysis : (TPA) Questions
A satellite is currently in a circular orbit with radius 32,714 km about the center of the earth.
Select for 0.5 km the increase, to the nearest whole kilometer, in the distance the satellite travels about the center of the earth during each revolution if the orbital radius of the satellite is increased by 0.5 km. And select for 1.5 km the increase, to the nearest whole kilometer, in the distance the satellite travels about the center of the earth during each revolution if the orbital radius of the satellite is increased by 1.5 km. Make only two selections, one in each column.
Phase 1: Owning the Dataset
Visualization
Let's draw the satellite's circular orbit:
Earth (center) ● /|\ / | \ r = 32,714 km / | \ ○----+----○ Circular orbit \ | / Distance per revolution = 2πr \ | / \ | / \|/
Key relationships:
- Distance traveled in one revolution = Circumference = \(2\pi r\)
- Current orbit radius: \(r_1 = 32,714\) km
- If radius increases by \(\Delta r\), new radius = \(r_1 + \Delta r\)
Phase 2: Understanding the Question
What we're asked to find:
- Part 1 (0.5 km): Increase in distance when radius increases by 0.5 km
- Part 2 (1.5 km): Increase in distance when radius increases by 1.5 km
Key Insight
When the radius increases from r to (r + Δr), the increase in circumference is:
- New circumference: \(2\pi(r + \Delta r)\)
- Old circumference: \(2\pi r\)
- Increase = \(2\pi(r + \Delta r) - 2\pi r = 2\pi\Delta r\)
Notice: The increase depends ONLY on \(\Delta r\), not on the original radius!
Phase 3: Finding the Answer
Calculations
For 0.5 km radius increase:
- Increase in distance = \(2\pi(0.5) = \pi\) km
- \(\pi \approx 3.14159...\) km
- To nearest whole kilometer: 3 km ✓
For 1.5 km radius increase:
- Increase in distance = \(2\pi(1.5) = 3\pi\) km
- \(3\pi \approx 9.42478...\) km
- To nearest whole kilometer: 9 km ✓
Verification with Answer Choices
Our answer choices are: [3km, 9km, 27km, 81km, 150km, 450km]
- 0.5 km → 3 km ✓ (matches first choice)
- 1.5 km → 9 km ✓ (matches second choice)
Phase 4: Solution
Final Answer:
- 0.5 km: 3km
- 1.5 km: 9km
The elegant mathematical principle here is that the increase in orbital distance is simply \(2\pi\) times the increase in radius, regardless of the initial orbit size. This makes our calculation beautifully simple!