A crane traveling at 15 mph must be able to stop in what distance?

• A. 32 feet
• B. 20 feet
• C. 40 feet
• D. 50 feet

Answer: (A)

Stopping distance depends on how fast you’re going and how hard you can brake—the faster you move, the more distance you need to stop, because you have more kinetic energy to dissipate.

At 15 mph, speed is about 22 feet per second. If the braking capability allows a deceleration of roughly 7.5 feet per second squared (about 0.23 g), the stopping distance is s = v^2/(2a) = 22^2 / (2×7.5) ≈ 32 feet. So about 32 feet is the distance needed to come to a stop under typical crane braking, which is why that option is the best choice.