A uniform ladder 15 ft long is leaning against a frictionless wall at an angle of 53° above the horizontal. The weight of the ladder is 30 pounds. A 75-lb boy climbs 6.0-ft up the ladder. What is the magnitude of the friction force exerted on the ladder by the floor?
a. 43 lb
b. 34 lb
c. 38 lb
d. 47 lb
e. 24 lb
b
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An enclosed chamber with sound absorbing walls has a 2.0 m × 1.0 m opening for an outside window. A loudspeaker is located outdoors,, 78 m away and facing the window
The intensity level of the sound entering the window space from the loudspeaker is 79 dB. Assume the acoustic output of the loudspeaker is uniform in all directions and that the acoustic energy incident upon the ground is completely absorbed and therefore is not reflected into the window. The threshold of hearing is 1.0 × 10-12 W/m2. The acoustic power entering through the window space is closest to A) 160 µW. B) 79 µW. C) 320 µW. D) 790 µW. E) 1600 µW.
Lenses that are thicker at the center than at the edge:
a. converge light. b. diverge light. c. redirect light by 90°. d. refract white light into the color spectrum. e. neither converge nor diverge light.
A slab of material 1 rests on the surface of a slab of material 2 . A light ray in material 1 has an angle of incidence of 30° on the interface between the materials, while the ray in material 2 has an angle of refraction of 45°. What is the critical angle of incidence for total internal reflection for a ray of light going from material 2 to material 1?
a. 30° b. 45° c. In this case there is no critical angle. d. At least one of the indices of refraction or its equivalent is needed to solve this problem.
Describe the evidence that best supports the Milankovitch hypothesis
What will be an ideal response?