How do scientists study the history of life on Earth?
A) by comparing present-day organisms with each other, and assuming past life had mixed traits of present-day organisms
B) by assuming that life in the past was just like present-day life
C) by using telescopes to look far away, and thus see what life was like in the past
D) by studying fossils, the preserved remains of past organisms
D
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A 2.0-kg object (the system) is lifted vertically through 3.00 m by a constant 150-N force. How much work did Earth do on the object during this process?
What will be an ideal response?
Melanie says that when a diver enters an underwater cave of height h, the pressure on her is no greater than ?Wgh. Rosalind says that if the bottom of the cave is a distance H below the water surface, the pressure on the soles of the diver's feet can reach ?WgH. Which one, if either, is correct? (The density of water is ?W.)
a. Melanie, because the roof of the cave absorbs the water pressure from above. b. Melanie, because only the fluid directly above any volume of the fluid can contribute to the pressure on that volume. c. Rosalind, because a fluid exerts equal pressure in all directions at a given depth. d. Rosalind, because the pressure also depends on the density, ?c, of the material above the cave roof, so that p = ?cg(H ? h) + ?Wgh. e. Melanie, because the pressure equals p = ?WgH ? ?cg(H ? h).
A human, running up stairs, can briefly use power of approximately
A. 0.01 horsepower B. 0.1 horsepower C. 0.2 horsepower D. 1 horsepower
Lenz's Law: A circular coil lies flat on a horizontal surface. A bar magnet is held above the center of the coil with its north pole pointing down. If the magnet is dropped from this position what is the direction of the induced current in the coil, as viewed from above?
A. counterclockwise B. clockwise C. An emf but no current is induced in the coil. D. There is no current in the coil.