Question

Reading of weighing machine when solid is immersed into it using a massless string is:

(a) 145N

(b) 130N

(c) 115N

(d) 100N

Solution

Buoyant force = Weight of displaced fluid = rhogV = 1000xx10xx3xx10^-3 = 30N

Weight of block will be balanced by tension in rope.

According to newton's 3rd law, block will apply equal and opposite force on water. The reaction of buoyancy on the beaker is respoible for the increase in weight.

Hence, reading shown by weighing machine will be:

100+30= 130N

Therefore, option(b) is correct.