School model

The beech school model of a regular quadrilateral pyramid has a base 20 cm long and 24 cm high. Calculate a) the surface of the pyramid in square decimeters, b) the mass of the pyramid in kilograms if the density of the beech is ρ = 0,8 g/cm ^ 3

Correct answer:

S =  14.4 dm2
m =  2.56 kg

Step-by-step explanation:

a=20 cm h=24 cm  S1=a2=202=400 cm2 h2=h2+(a/2)2=242+(20/2)2=26 cm  S2=2a h2=220 26=260 cm2  S3=S1+4 S2=400+4 260=1440 cm2  S=S3 dm2=S3:100  dm2=1440:100  dm2=14.4 dm2=572 dm2=14.4 dm2
ρ=0.8 g/cm3  V=31 S1 h=31 400 24=3200 cm3  m1=V ρ=3200 0.8=2560 g  m=m1 kg=m1:1000  kg=2560:1000  kg=2.56 kg=2564 kg=2.56 kg



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