A bat, flying at 5.00 m/s toward a wall, emits a chirp at 50.0 kHz. If the wall
ID: 1613094 • Letter: A
Question
A bat, flying at 5.00 m/s toward a wall, emits a chirp at 50.0 kHz. If the wall reflects this sound pulse, what is the frequency of the echo received by the bat? (nu_sound = 340 m/s) a. 51.5 kHz b. 51.2 kHz c. 40.8 kHz d. 46.9 kHz e. 50.5 kHz A child sits on a swing supported by ropes of length 3.0 m. With what frequency will she need to apply the driving force to maintain swinging? a. 0.29 Hz b. 0.48 Hz c. 2.1Hz d. 3.5 Hz The electromagnetic radiation that causes tanning: a. can produce cancer. b. is the same one that gives us warmth. c. rarely passes through glass windows. d. is absorbed by ozone. e. is all of the above.Explanation / Answer
Given
12
bat flying towards a wall with velocity vs = 5 m/s, emits the frequency f = 50 kHz
if the wall reflects the sound pulse then the frequency of the echi that the bat can observe is
from dopplers effect
f' = f (v+vs/v-v0)
= 50*10^3(340+5/340-0) Hz = 50.735 kHz
answer from the options is e. 50.5 kHz
13
length of the rope is l = 3 m
timeperiod of pendulum is T = 2pi sqrt(l/g) = 2pi sqrt(3/9.8)
the frequecncy is f = 1/T = 1/3.4763817222631 = 0.2876554Hz
answer is option a 0.29 Hz
14.
the electromagnetic radiation that causes tanning is all of the above
answer is e
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