Question

Paralelipiped
L=15 cm
l= 10 cm
h= 5 cm
Densitatea= 7800 kg/m3
Presiunea maxima=?
Presiunea minima=?

Answer 1

L=15 cm=0,15 m

l=10 cm=0,1 m

h=5 cm=0,05 m

V=Llh=0,15*0,1*0,05=0,00075 m³

ρ=m/V=>m=ρV=7800*0,00075=5,85 kg

G=mg=5,85*10=58,5 N

Smin=L*l=0,15*0,1=0,015 m²

Smax=h*l=0,05*0,1=0,005 m²

Pmin=G/Smin=58,5/0,015=3900 Pa

Pmax=G/Smax=58,5/0,005=11700 Pa

Answer 2

P = F/S

F = G = m×g

ρ = m/V => m = ρ×V

V = 15cm×10cm×5cm = 750 cm³

ρ = 7800 kg/m³ = 7,8 g/cm³

m = 7,8 g/cm³×750 cm³ = 5850 g = 5,85 kg

G = 5,85kg×10N/kg = 58,5 N

1)

S(minima ) = 5cm×10cm = 50 cm² = 0,005 m²

P(maxima) = 58,5N/0,005m² = 11 700 Pa

2)

S(maxima) = 15cm×10cm = 150 cm² = 0,015 m²

P(minima) = 58,5N/0,015m² = 3900 Pa

Obs. Cu cat suprafata este mai MICA presiunea este mai MARE.