Bob has just finished climbing a sheer cliff above a beach, and wants to figure
ID: 2242316 • Letter: B
Question
Bob has just finished climbing a sheer cliff above a beach, and wants to figure out how high he climbed. All he has to use, however, is a baseball, a stopwatch, and a friend on the ground below with a long measuring tape. Bob is a pitcher, and knows that the fastest he can throw the ball is about 32.9 m/s. Bob starts the stopwatch as he throws the ball (with no way to measure the ball's initial trajectory), and watches carefully. The ball rises and then falls, and after 0.910 seconds the ball is once again level with Bob. Bob can't see well enough to time when the ball hits the ground. Bob's friend then measures that the ball landed 127 m from the base of the cliff. How high up is Bob, if the ball started from exactly 2 m above the edge of the cliff?
Explanation / Answer
ou start this problem by realizing that of the .910 seconds the ball spends above eye level, .355s is in upward motion and .355s is in downward motion, with the vertical component of velocity being equal to zero .355s after release. Thus you can multiply -9.8m/s2 by .355 seconds and find that the ball has a vertical velocity component of -3.47 m/s when it crosses Bob