What evidence leads scientists to conclude that life was present on Earth within a billion years of its formation?
A) Such early existence of life is the only way to explain the variety of life-forms seen today.
B) Fossil evidence of life dates back to this time.
C) Studies of DNA indicate that life must have been present by that time.
B) Fossil evidence of life dates back to this time.
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Design a composite material made of epoxy and uniaxial E-glass fibers that has an axial elastic modulus of 50 GPa. The epoxy resin has an elastic modulus of 5 GPa, and the E-glass fibers have an elastic modulus of 72.4 GPa.
(a) What is the volum fraction of fibers and matrix in this composite? (b) What is the transverse elastic modulus of this material?
The size of a black hole, its Schwarzschild radius, is simply proportional to its _____
A) mass B) luminosity C) temperature D) density
A long cylinder (radius = 3.0 cm) is filled with a nonconducting material which carries a uniform charge density of 1.3 ?C/m3 . Determine the electric flux through a spherical surface (radius = 2.0 cm) which has a point on the axis of the cylinder as its center
a. 5.7 N / m2/C b. 4.9 N / m2/C c. 6.4 N / m2/C d. 7.2 N / m2/C e. 15 N / m2/C
A spring (k = 600 N/m) is at the bottom of a frictionless plane that makes an angle of 30° with the horizontal. The upper end of the spring is depressed 0.10 m, and a 2.0-kg block is placed against the depressed spring. The system is then released from rest. What is the kinetic energy of the block at the instant it has traveled 0.10 m and the spring has returned to its uncompressed length?
a. 2.0 J b. 1.8 J c. 2.2 J d. 1.6 J e. 1.0 J