Question

A beaker which is half – filled with water is put on a platform balance which is set to zero. As shown in the figure, a 800g mass is immersed partially in water using a spring balance. Find the reading of the platform balance if the spring balance reads 300g.

A. $200g$
B. $300g$
C. $500g$
D. $800g$

Answer 1

Hint The reading shown by the platform balance is the buoyant force exerted by the liquid on block.
So, the exerted buoyant force is equal to the difference of actual weight and approximate weight. Then, we can get the reading of spring balance.

Complete step-by-step solution :The Buoyant force can be defined as an upward force which is experienced by when an object is immersed in liquid. This Buoyant force causes Buoyancy which is the phenomenon of experiencing an upward force. The S.I unit of Buoyant Force is Newton which is denoted by $N.$
The spring balance is the weighing scale which has hook at its one end which used to attach an object and have spring attached at another end. The spring balance opposed the force of gravity with force of a spring to measure the weight of an object.
Now, according to the question it is given that,
Actual weight, $W = 800g$
Approximate weight, $w = 300g$
The reading shown by platform balance will be the buoyant force exerted by liquid on block.
So, the reading shown by platform balance = Buoyant Force
$\therefore$Reading shown by the platform balance $= W - w$
$\Rightarrow 800g - 300g = 500g$
Thus, the reading shown by weighing machine is $500g$.
Hence, option (C) is the correct answer.

Note:- The spring balance uses the principle of Hooke’s Law which states that, “the stress of object or body is proportional to the corresponding strain, if and only if the deformation is small”. Difference between the actual length and natural length of spring balance is the extension of spring. It can also be said as no load condition.