An electron moves in a region where the magnetic field is uniform and has a magnitude of 80 ?T. The electron follows a helical path which has a pitch of 9.0 mm and a radius of 2.0 mm. What is the speed of this electron as it moves in this region?
A. 48 km/s
B. 28 km/s
C. 20 km/s
D. 35 km/s
E. 8.0 km/s
Answer: D
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Lead has a shear modulus of 
and a density of 
What is the velocity of shear waves in lead?
A. 691 m/s B. 621 m/s C. 575 m/s D. 521 m/s E. 487 m/s
A girl is sitting on the edge of a pier with her legs dangling over the water. Her soles are 80.0 cm above the surface of the water. A boy in the water looks up at her feet and wants to touch them with a reed. (nwater = 1.333.) He will see her soles as being
A. right at the water surface. B. 53.3 cm above the water surface. C. exactly 80.0 cm above the water surface. D. 107 cm above the water surface. E. an infinite distance above the water surface.
The carbon dioxide cycle is important to Earth because it
A) helps sustain the planet's plant base. B) has been recognized by the Nobel Prize award committee. C) and the oceans are critical in moderating and regulating the Earth's temperatures. D) prevents the gradual buildup of oxygen, which would eventually lead to a combustible atmosphere.
What observation has prompted astronomers to ponder the possible existence of dark energy?
a. discovery of quasars b. discovery of superclusters c. supernovae appear fainter than expected at large redshifts d. uniform nature of the cosmic microwave background (CMB)