A 20 N metal bloc A.36 N

B. 60 N

C. 44 N

D. 56 N

Here, we balance the vertical forces to find the reading in the weighing machine.

Weight of the block, w=20N

Weight of the water, W= 40 N

Weight after immersion, w’= 16N

Therefore, the buoyant force, F_B= 20 -16 = 4 N

This is the force exerted by the water on the block upwards. Equal and opposite force is exerted by the block on the water.

Thus the total vertical force on the water, F= W+F_B = 40+4= 44N.