Question

The work is done in lifting a body of mass 20 kg and specific gravity 3.2 to a height of 8 m in
water is,

• A. $110J$
• B. $1600J$
• C. $500J$
• D. $1100J$

Answer 1

Answer: (D)

$1100J$

It is given that,

Mass of body $=20kg$

Specific gravity $=3.2$

The mass of the water that will be displaced by body:

$\frac{20}{3.2}=6.25kg$

The force exert on the body downwards because of gravity :

$20\times 10=200N$

The force exerted by water in upward direction:

$6.25\times 10=62.5N$

Thus, total force $=200-62.5=137.5N$

The work done in lifting a body to a height of $8m$:

$137.5\times 8=1100J$

Hence, the work done in lifting a body to a given height is $1100J$