Question

A piece of wood is held under water. The upthrust on it will be ___________the weight of the wood piece.
A) more than
B) less than
C) same
D) none of the above

Answer 1

Hint: We define the question by using the Archimedes principle. It states that it is based in terms of forces. Up thrust means that the upward force acts by a fluid that opposes the weight of the immersed objects. The upthrust force depends on the volume of the wood, the weight of the wood, and acceleration due to gravity.

Complete step by step solution:
Generally, we know that the weight of the wood is low specific density. So it depends on the weight of the wood. If the density of the wood is lower than the density of the water, here up thrust will be more. So the wood floats on the water. In case, the density of the wood is greater than the density of the water the upthrust will be less. So the wood is dipped under the water.
In other cases, the density of the wood is the same as the density of the water. Here the wood is neither dipped nor float in the water which means half part of the wood will be in the water and the remaining half part of the wood will be in the surface of the water. In the upthrust force buoyancy force acting on it.
Here, the wooden piece is under the water because the upthrust force acting on the wood under the water is less than the weight of the wooden piece.

Hence from the above option, the option B is correct.

Note: From the question, we know that the upthrust means the upward forces pushing the object from down to up. Up thrust is also known as buoyancy. There are three types of buoyancy forces. If the object floats, a positive buoyancy force is acted on it. If the object is under the water, Negative buoyancy acts on it. Neutral buoyancy means that the weight of the object and water are equal, neutral buoyancy acts on the object.