Question

A $20N$ metal block is suspended by a spring balance. A beaker containing some water is placed on a weighing machine which reads $40N$. The spring balance is now lowered so that the block gets immersed in the water. The spring balance now reads $16N$. The reading of the weighing machine will be

• A. $36N$
• B. $60N$
• C. $44N$
• D. $56N$

Answer 1

The correct option is C $44N$

given,

weight of metal block in air ($W_1$) = 20N

weight of water ($W_2$) = 40N

reading of spring balance when block immersed in water = 16N

we know that when block is placed in water then buoyancy forcce acts on block in upward direction

let $F_s$ be spring force.

let $F_b$ be buoyancy force accting on the block.

let $F_W$ be reading of weighing maching when block is inside is the water

by free body diagram ,

$F_s$ +$F_b$ =$W_1$

16+$F_b$=20

$F_b$=4N

therefore buoyancy force is 4N

now

$W_2$ + $F_b$ = $F_W$

40+4 = $F_W$

therefore $F_W$= 44N

there option C is correct