What force must be applied to evenly lift a granite slab weighing 1.5 tons and a volume of 0.6 m3 from the bottom of the lake?

Given:

m = 1.5 tons is the mass of a granite slab lying on the bottom of the lake;

V = 0.6 cubic meters – the volume of the granite slab;

ro = 1000 kg / m3 – water density.

It is required to determine F (Newton) – what force must be applied in order to evenly lift a granite slab from the bottom of the lake.

Let’s convert the units of measurement of mass to the SI system:

m = 1.5 tons = 1.5 * 1000 = 1500 kilograms.

Since in the condition of the problem it is said that the plate must be lifted uniformly (that is, with a constant speed), then, according to Newton’s first law:

F = F gravity – Farchimedes;

F = m * g – ro * V * g, where g = 10 Newton / kilogram (approximate value);

F = g * (m – ro * V);

F = 10 * (1500 – 1000 * 0.6) = 10 * (1500 – 600) = 10 * 900 = 9000 Newton (9 kN).

Answer: to evenly lift the granite slab from the bottom of the lake, it is necessary to apply a force equal to 9 kN.