AP Physics 1 Question 104: Answer and Explanation

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Question: 104


In the laboratory, a 0.5-kg cart collides with a fixed wall, as shown in the preceding diagram. The collision is recorded with a video camera that takes 20 frames per second. A student analyzes the video, placing a dot at the center of mass of the cart in each frame. The analysis is shown above.

About how fast was the cart moving before the collision?

  • A. 0.25 m/s
  • B. 4.0 m/s
  • C. 0.20 m/s
  • D. 5.0 m/s

Correct Answer: B


B-The dots divide the 1-meter distance into five parts. In the time between dots, the cart travels 1/5 of a meter, or 0.2 m. The time between dots is 1/20 of a second, or 0.05 s. At constant speed, the speed is given by distance/time: 0.20 m/0.05 s = 4 m/s.