Suspended from a spring balance is a 20 N metal block. A beaker containing some water is placed on a weighing machine, which initially reads 40 N . The spring balance is subsequently lowered so that the block becomes immersed in the water. The spring balance then reads 16 N . The reading on the weighing machine will be

Step-by-step solution

Initial reading of the spring balance is 20 N and the final reading is 16 N . The loss in weight of the block is equal to the buoyant force exerted by the water. Buoyant force F_B = 20 N - 16 N = 4 N . According to Newton's third law, the block exerts an equal and opposite downward force of 4 N on the water. The total downward force on the weighing machine increases by the magnitude of this reaction force. New reading on the weighing machine = 40 N + 4 N = 44 N .