In a four-stroke cycle engine with a 6-inch stroke operating at 2,000 RPM, when is the piston movement at maximum velocity?

The correct choice highlights that in a four-stroke cycle engine, the piston reaches its maximum velocity 90 degrees after top dead center (TDC). This occurs because of the relationship between crankshaft rotation and piston movement.

At TDC, the piston momentarily comes to a stop before changing direction to begin its downward movement during the power stroke. As the crankshaft continues to turn, the linear velocity of the piston increases, reaching its peak around 90 degrees after TDC. At this point, the angle between the crankshaft and connecting rod allows for maximum leverage, translating to maximum linear speed of the piston.

Understanding the four-stroke cycle is crucial here. The four strokes consist of intake, compression, power, and exhaust, with each rotation of the crankshaft corresponding to one complete cycle. The transition beyond TDC is where the potential energy from combustion is converted into kinetic energy, propelling the piston downward at the highest speed.

Therefore, the answer accurately captures the timing of maximum piston velocity in the cycle, which occurs not at TDC (where velocity is zero), but rather as the piston descends, maximizing shortly thereafter during the downward motion.