A bat, flying due east at 2 m/s, emits a shriek that is reflected back to it from an oncoming insect flying directly toward the bat at 4 m/s. The insect is 20 m from the bat at the instant the shriek is emitted. Sound travels 340 m/s in air
After what elapsed time does the bat hear the reflected echo?
57 milliseconds
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What determines how rapidly a star burns up its fuel?
A. the temperature in its core B. its mass C. its luminosity D. the pressure in its core E. All of these choices are correct.
The weak interaction is mediated by
A. gluon. B. photon. C. mesons. D. W+, W-, Z0. E. leptons.
A boat that contains a heavy anchor floats in a small lake. If the anchor is thrown overboard, but the rope isn't long enough for the anchor to touch bottom, which of the following will happen?
(i) The level of the water in the lake will go down slightly. (ii) The level of the water in the lake will go up slightly. (iii) The level of the water in the lake will stay exactly the same. (iv) The waterline on the boat will go up (that is, the boat will sink slightly). (v) The waterline on the boat will go down (that is, the boat will rise slightly). (vi) The water line on the boat will stay the same.
1.(i) and (v) 2.(ii) and (iv) 3.(iii) and (vi) 4.(iii) and (v)A concave mirror has a 12 cm tall object placed 40 cm in front of it. An image forms 60 cm in front of the mirror. What is the size and orientation of the image?
A. 8.0 cm, inverted B. 8.0 cm, upright C. 18 cm, inverted D. 18 cm, upright E. 24 cm, upright