AP Physics 1 Question 91: Answer and Explanation

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Question: 91

1. The Space Shuttle orbits 300 km above Earth’s surface; Earth’s radius is 6,400 km. What is the gravitational acceleration experienced by the Space Shuttle?

  • A. Zero
  • B. 4.9 m/s2
  • C. 9.8 m/s2
  • D. 8.9 m/s2

Correct Answer: D


D-The gravitational acceleration is given by GM/d2, where d is the Space Shuttle's distance to Earth's center. You don't know values for G and M, nor do you need to know them. You do know that at Earth's surface, 6,400 km from the center, the gravitational acceleration is 9.8 m/s2. To calculate using this equation at the height of the Space Shuttle, the numerator remains the same; however, the denominator increases from (6,400 km)2 to (6,700 km)2, a difference of about 8%. (Try it in your calculator if you don't believe me.) Thus, the gravitational acceleration will decrease by about 8%, giving choice D. (Yes, things seem "weightless" in the Space Shuttle. That's not because g = 0 there, but because everything inside the shuttle, including the shuttle itself, is in free fall, accelerating at 8.9 m/s/s toward the center of Earth.)