The rst word spoken on the surface of the Moon after

Chapter 2, Problem 122

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The rst word spoken on the surface of the Moon after Apollo 15landed on July 30, 1971, was Bam! This was James Irwins involuntary reaction to their rather bone-jarring touchdown. We did hit harder than any of the other ights! says Irwin. And I was startled, obviously, when I said, Bam! The reason for the rm touchdown of Apollo 15, as pilot David Scott later characterized it, was that the rocket engine was shut off a bit earlier than planned, when the lander was still 4.30 ft above the lunar surface and moving downward with a speed of 0.500 ft/s. From that point on the lander descended in lunar free fall, with an acceleration of 1.62 m/s2. As a result, the landing speed of Apollo 15was by far the largest of any of the Apollo missions. In comparison, Neil Armstrongs landing speed on Apollo 11 was the lowest at 1.7 ft/she didnt shut off the engine until the footpads were actually on the surface. Apollos 12, 14, and 17 all landed with speeds between 3.0 and 3.5 ft/s. To better understand the descent of Apollo 15, we show its trajectory during the nal stages of landing in Figure 237(a). In Figure 237 (b) we show a variety of speed-versus-time plots. How long did it take for the lander to drop the nal 4.30 ft to the Moons surface? A. 1.18 s B. 1.37 s C. 1.78 s D. 2.36 s