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Question
A plastic cube is released into the water. Will it sink or come to the surface of the water?
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Solution
When a plastic cube is released into water, it will come to the surface and float if its density is lower than the density of water. This happens because of buoyancy. Water exerts an upward buoyant force on the cube, and if this force is equal to or greater than the cube’s weight, the cube floats.
In this experiment, the plastic cube floats because it is less dense than water. In contrast, a glass cube usually sinks because its density is greater than that of water, so its weight is greater than the buoyant force acting on it.
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body D having density 0.85 g m-3
Why does it happen?
A ship dips to a larger depth in fresh water as compared to marine water.
State whether pressure is a scalar or vector?
Describe a simple experiment to demonstrate that a liquid enclosed in a vessel exerts pressure in all directions.
The diagram below in Fig. 4.12 shows a device which makes the use of the principle of transmission of pressure.
- Name the parts labelled by the letters X and Y.
- Describe what happens to valves A and B and to the quantity of water in the two cylinders when the lever arm is moved down.
- Give reasons for what happens to valves A and B in part (ii).
- What happens when the release valve is opened?
- What happens to valve B in cylinder P when the lever arm is moved up?
- Give a reason for your answer in part (v).
- State one use of the above device.
Complete the following sentence :
Pressure of a liquid at a given depth is .................. To the density of the liquid.
A simple U tube contains mercury to the same level in both of its arms. If water is poured to a height of 13.6 cm in one arm, how much will be the rise in mercury level in the other arm?
Given : density of mercury = 13.6 x 103 kg m-3 and density of water = 103 kg m-3.
Two identical pieces, one of ice (density = 900kg per meter cube) and other wood (density = 300kg per meter cube) float on water.
- Which of the two will have more volume submerged inside water
- Which of two will experience more upthrust due to water.
Is pressure a vector quantity?
Assertion (A): The buoyant force on a submerged rigid object can be considered to be acting at the center of mass of the object.
Reason (R): In rigid body, force distributed uniformly through its volume can be considered to be acting at the centre of mass of the body.
