How to Calculate Distance, Speed, and Displacement for the GED Science Test - dummies

How to Calculate Distance, Speed, and Displacement for the GED Science Test

By Murray Shukyn, Achim K. Krull

The GED Science test will have some physics calculations questions. Knowing some key formulas will help you be prepared for test day. In physics, motion is measured in terms of distance, speed, displacement, velocity, and acceleration:

  • Acceleration: Rate of change in velocity, typically measured in meters per second per second (m/s/s or m/s2).

  • Displacement: The net change in an object’s position and direction.

  • Distance: The space between two positions.

  • Speed: The rate (typically average rate) at which an object moves.

  • Velocity: Speed in a certain direction.

Note the difference between scalar and vector quantities. Distance is a scalar quantity indicating how far an object has traveled, whereas displacement is a vector quantity indicating the change in an object’s position. If you run one lap around a quarter-mile track, you run a distance of 0.25 miles, but your displacement is 0 because you’re back where you started.

Likewise, speed is scalar, whereas velocity is vector. If you run a 6-minute mile on that same oval track, you ran 10 miles per hour, but your velocity is 0 because you’re back where you started.

To calculate distance, average speed, or time when given the other two values, use the following formula: s = d/t

  1. An eagle flies due east 40 miles per hour for 1 hour and 30 minutes and then 10 miles in the opposite direction at 20 miles per hour. How far did it fly? _________ miles

  2. What is the eagle’s displacement? _________ miles

  3. Which of the following represents the eagle’s velocity?

    • (A) 40 mph

    • (B) 40 mph east

    • (C) 25 mph

    • (D) 25 mph east

Check your answers:

  1. The eagle flew 40 miles in 1 hour plus 20 miles in a half-hour plus 10 miles, for a total distance of 70 miles.

  2. The eagle flew 40 miles east in 1 hour plus another 20 miles east in a half-hour minus 10 miles west, so its displacement is 60 – 10 = 50 miles.

  3. The eagle’s net change in position is 50 miles east, and it was flying for 2 hours, so its velocity is 50 ÷ 2 = 25 miles per hour east, Choice (D).