Floatation – Very Short Answer Questions
1. State the principle of floatation.
A body floats if the weight of the liquid displaced equals the weight of the body.
2. A piece of wood weighs 70 gf in air. It is lowered into water. What is the reading on spring balance?
The reading will be 0 because the wood floats and apparent weight becomes zero.
3. How does the density ρs of a substance determine whether it will float or sink?
If ρs < ρliquid, it floats; if ρs > ρliquid, it sinks.
4. A body floats with a part submerged. Is its weight more, equal to, or less than the upthrust?
The weight is equal to the upthrust when it floats.
5. What can you say about the average density of a ship that floats?
The average density of the ship is less than that of water.
6. Two identical pieces, one of ice and one of wood, float in water. Which displaces more water and experiences more upthrust?
Ice displaces more water and experiences more upthrust because it is denser than wood.
7. A piece of ice melts in water. Why doesn’t water level change?
No change in level of water on melting a floating piece of ice: When a floating piece of ice melts into water, it contracts by the volume equal to the volume of ice piece above the water surface while floating on it. Hence the level of water does not change when the ice floating on it melts.
8. A buoy is held underwater by a string. Name the three forces acting and their directions.
1) Weight (downward), 2) Tension in thread (downward), 3) Upthrust (upward).
