Final answer:
The tension in the string decreases when a Ping-Pong ball is replaced by an object with the same size and shape but lesser weight, since less tension is needed to balance the reduced upward buoyant force against the object's weight.
"the correct option is approximately option C"
Step-by-step explanation:
When a Ping-Pong ball that ordinarily floats is submerged in water and held by a string, it experiences a buoyant force pushing it upward. If this Ping-Pong ball is replaced with another object of the same size and shape, but lesser weight, the tension in the string will decrease. This is because the buoyant force acting upon both objects remains the same (assuming they displace the same volume of water), but the upward force needed to balance the lesser weight of the new object is lower, thus reducing the tension necessary in the string to keep it submerged.
Comparing a helium balloon tugging upward on its string due to air's buoyant effect and a heavy object like an anchor being partly supported by water, illustrates the principle of buoyancy affecting tension in different mediums. In both cases, the buoyant force moves in the opposite direction of gravity, and the difference between the two forces determines the tension in the string.
When the ball moves over the top of a vertical circle at its slowest possible speed so that the tension in the string is negligible, the tension in the string at the bottom of the circle increases due to the ball's weight and the centripetal force needed to keep it in circular motion. An object that is lighter would yield less tension when held at the bottom of the circle or when submerged in a fluid.