AP Physics 1 Question 399: Answer and Explanation

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Question: 399

7. A student attaches a 1.5 kg mass to a 40 cm long string. The student then begins to whirl the mass in a horizontal circle with increasing speed. If the string snaps when the mass has a speed of 6 m/s, what is the breaking strength of the string?

  • A. 22.5 N
  • B. 135 N
  • C. 240 N
  • D. 360 N

Correct Answer: B



As the mass is whirled in a horizontal circle, it is the tension force that snapped the string and is equal to the breaking strength when the mass is traveling at 6 m/s. As the tension force is the only force acting in the horizontal direction, it is also producing centripetal force and can be calculated as follows: