From the mathematical functions (with x is in metres, t in seconds), select thos
ID: 1524823 • Letter: F
Question
From the mathematical functions (with x is in metres, t in seconds), select those which correspond to each of the five motions below . For example, if functions A and G satisfy motion 1, function C satisfies motion 2 and none of the functions satisfies motions 3, 4 and 5, enter AGCNNN. (Note that the answers for each motion must be in alphabetical order.)
A) y(x,t) = 0.4 sin(2x)cos(6t)0.8 sin(x)cos(x)cos(6t)
B) y(x,t) = 0.4 cos(2x)sin(6t)
C) y(x,t) = 0.4
D) y(x,t) = 0.2 sin(3x9t)
E) y(x,t) = 0.4 cos(x)sin(t/3)
F) y(x,t) = 0.4 sin(2x)cos(2t/6)
G) y(x,t) = 0.8/(2+(3x+9t)2)
H) y(x,t) = 0.4/(1+(x3t)2)
N) none of the above
1) A motion in which the movement of the medium corresponds to a wavelength of 1 m.
2) A harmonic travelling wave or wave pulse which causes the medium to oscillate with a standard frequency of 3 Hz.
3) A standing wave that causes the medium to oscillate with a standard frequency of 3 Hz.
4) A harmonic wave or wave pulse travelling in the positive x direction at 3 m/s.
5) A motion in which the medium at x = 0 m is fixed, i.e., it is unable to move.
Explanation / Answer
equation of a standing wave; y= a sin kx cos wt
k= 2 pi/lambda and w= 2 pi/T oe w= 2 pi f
1) A motion in which the movement of the medium corresponds to a wavelength of 1 m
B) y(x,t) = 0.4 cos(2x)sin(6t)
here 2= 2 pi/lambda, so lambda= 1m
F) y(x,t) = 0.4 sin(2x)cos(2t/6)
here 2= 2 pi/lambda, so lambda= 1m
so both function B and F satisfy 1
(2) A harmonic travelling wave or wave pulse which causes the medium to oscillate with a standard frequency of 3 Hz.
none of the gven functions represents a travelling wave with a freq of 3 Hz , so N.
(3)A standing wave that causes the medium to oscillate with a standard frequency of 3 Hz
B) y(x,t) = 0.4 cos(2x)sin(6t)
2f=6
f= 3 Hz, so for 3, we have B .
4) A harmonic wave or wave pulse travelling in the positive x direction at 3 m/s.
D) y(x,t) = 0.2 sin(3x9t)
2 pi /lambda= 3
lambda= 2pi/3
2pi f= 9
f= 9/2pi
wave velocity= f* lambda
v=(9/2pi)* (2 pi/3)
v= 3m/s
so for 4, it is D .
(5) A motion in which the medium at x = 0 m is fixed, i.e., it is unable to move.
C) y(x,t) = 0.4
we have C .
so the answer is BFNBDC
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