PSAT Math Multiple-Choice Question 288: Answer and Explanation

Question: 288

If a baseball is 15 feet high when a stopwatch reads 3.2 seconds and 30 feet high when the stopwatch reads 3.6 seconds, what is its vertical speed (that is, rate of change of height)? Assume the speed is constant between 3.2 and 3.6 seconds on the stopwatch.

• A. 0.03 feet per second
• B. 15 feet per second
• C. 37.5 feet per second
• D. 75 feet per second

Correct Answer: C

Explanation:

Its vertical speed is 37.5 feet per second. Use the rate-of-change formula to calculate the change in height over the duration of time (change of time):

= = = 37.5 feet per second

See Lesson: Ratios, Proportions, and Percentages.