UNIVERSE (LOOSELEAF):STARS+GALAXIES
UNIVERSE (LOOSELEAF):STARS+GALAXIES
6th Edition
ISBN: 9781319115043
Author: Freedman
Publisher: MAC HIGHER
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Chapter 25, Problem 41Q
To determine

(a)

The critical density of matter in the universe.

Expert Solution
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Answer to Problem 41Q

The critical density of matter in the universe is 4.699×1038kg/m3.

Explanation of Solution

Given:

The Hubble constant is, H1=50km/sMpc.

Formula used:

The critical density of matter in the universe is given by,

ρc=3H28πG

Calculation:

The gravitational constant is, G=6.67×1011m3/kgs2

The critical density of matter in the universe is calculated as,

ρc=3H28πG=3 ( 50 kmMpc/ sMpc )28π( 6.67× 10 11 m 3 / kg s 2 )=3 ( 50 km/ sMpc )2 ( 1Mpc 3.0856× 10 13 Mkm )28π( 6.67× 10 11 m 3 / kg s 2 )=3 ( 50 km/ sMpc )2 ( 1Mpc 3.0856× 10 13 Mkm( 10 6 km 1Mkm ) )2( 167.63 m 3 / kg s 2 )

Solve further,

ρc=3 ( 16.20× 10 19 s 1 )2( 167.63 m 3 / kg s 2 )=787.738× 10 38s 2( 167.63 m 3 / kg s 2 )=4.699×1038kg/m3

Conclusion:

The critical density of matter in the universe is 4.699×1038kg/m3.

To determine

(b)

The critical density of matter in the universe.

Expert Solution
Check Mark

Answer to Problem 41Q

The critical density of matter in the universe is 6.266×1038kg/m3.

Explanation of Solution

Given:

The Hubble constant is, H1=100km/sMpc.

Calculation:

The critical density of matter in the universe is calculated as,

ρc=3H28πG=3 ( 100 kmMpc/ sMpc )28π( 6.67× 10 11 m 3 / kg s 2 )=3 ( 100 km/ sMpc )2 ( 1Mpc 3.0856× 10 13 Mkm )28π( 6.67× 10 11 m 3 / kg s 2 )=3 ( 100 km/ sMpc )2 ( 1Mpc 3.0856× 10 13 Mkm( 10 6 km 1Mkm ) )2( 167.63 m 3 / kg s 2 )

Solve further,

ρc=3 ( 32.40× 10 19 s 1 )2( 167.63 m 3 / kg s 2 )=1050.317× 10 38s 2( 167.63 m 3 / kg s 2 )=6.266×1038kg/m3

Conclusion:

The critical density of matter in the universe is 6.266×1038kg/m3.

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