At what speed must a crankshaft turn if each cylinder of a four-stroke cycle engine is to be fired 200 times a minute?

To determine the speed at which the crankshaft must turn so that each cylinder of a four-stroke cycle engine fires 200 times a minute, it's important to understand how four-stroke engines operate. In a four-stroke engine, each cylinder completes a full cycle (intake, compression, power, exhaust) every two revolutions of the crankshaft.

Since there are 200 firings (or power strokes) per minute for each cylinder, and each cylinder requires two revolutions to complete its cycle, the crankshaft must rotate at a speed that is twice the firing rate of the cylinders. Thus, the correct speed for the crankshaft can be calculated by multiplying the firing rate by 2:

200 firings per minute × 2 (because it takes 2 revolutions to complete the cycle) = 400 RPM.

This calculation clearly shows that for each cylinder to fire 200 times in one minute, the crankshaft must indeed be turning at 400 revolutions per minute. This understanding reinforces the basic principles of four-stroke engine mechanics and ensures that you grasp how crankshaft speed relates to cylinder firing rates.