A block with dimensions of 10 x 5 x 20 cm is made of a substance with a density of 3000 kg / m3.

A block with dimensions of 10 x 5 x 20 cm is made of a substance with a density of 3000 kg / m3. There is an air cavity inside the bar, the volume of which is 40% less than the volume of the bar. Determine the force of gravity acting on the block if it is on your table.

Given: V = 10 * 5 * 20 centimeters;

ρ = 3000 kg / m3;

Find: Fт -?

Solution:

First, let’s calculate the volume of the bar: Vb = 0.10 m * 0.05 m * 0.20 m = 0.001 m³;
Further, we calculate the volume of the cavity Vp = 0.40 * 0.001 m³ = 0.0004 m³;

Substance in the bar: Vw = Vb – Vp;
Vw = 0.001 m³ – 0.0004 m³ = 0.0006 m³;
Mass: m = ρ * Vw = 3000 kg / m³ * 0.0006 m³ = 1.8 kg;
Ft = g * m = 10 N / kg * 1.8 kg = 18 N;

Answer: Ft = 18 N.