Example 015
Two balls, one 15 cm in diameter and the other 10 cm in diameter, are placed in a
cylindrical jar 20 cm in diameter, as shown in Figure 014. Find the volume of water
necessary to cover them.
x=2057.5x=2057.5
x=7.5 cmx=7.5 cm
h2+x2=(5+7.5)2h2+x2=(5+7.5)2
h2+7.52=12.52h2+7.52=12.52
h=10 cmh=10 cm
Depth of water
H=7.5+h+5H=7.5+h+5
H=7.5+10+5H=7.5+10+5
H=22.5 cmH=22.5 cm
Volume of water
Vwater=VHVballsVwater=VHVballs
Vwater=14(202)(22.5)43(7.53+53)Vwater=14(202)(22.5)43(7.53+53)
Vwater=4777.84 cm3Vwater=4777.84 cm3
answer
Example 014
A boy who had discovered that 20 mm marbles fitted snugly into the bottom of a
cylindrical jar, dropped in a fourth on top of the three and poured water enough into the
jar to just cover them. How much water did he use?
The lines connecting the center of marbles will form into a regular tetrahedron of edge
20 cm.
From triangle ABC
cos30=10AEcos30=10AE
AE=10cos30=1032AE=10cos30=1032
AE=11.55 mmAE=11.55 mm
CE=AECE=AE
CE=11.55 mmCE=11.55 mm
Radius of cylinder
R=10+AE=10+11.55R=10+AE=10+11.55
R=21.55 mmR=21.55 mm
Solving for h from right triangle CED
h2+CE2=CD2h2+CE2=CD2
h2+11.552=202h2+11.552=202
h=16.33 mmh=16.33 mm
Depth of water
H=20+h=20+16.33H=20+h=20+16.33
H=36.33 mm
H=36.33 mm
Volume of water
Vwater=Vcylinder4VmarbleVwater=Vcylinder4Vmarble
Vwater=(21.552)(36.33)4[43(103)]Vwater=(21.552)(36.33)4[43(103)]
Vwater=36248.98 mm3Vwater=36248.98 mm3
answer
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