Quote:
Originally Posted by Kayee
can someone help me with 2 questions? been stuck for a while
the answer is c
the answer is b and I dont know what should i hold as a constant
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For the first one: the particle cannot be travelling on the x-axis since it only ever moves up and down (i.e. y-axis), so eliminate all answers that say "in the ___ x-direction". Next, eliminate the option of it being zero because the particle is not at a local max/min at t=0 (the velocity, which is the derivative of this curve, can only be zero at a local max/min). Now, since the wave equation is y(x,t)=4sin(2x-3t), we know that the
wave is moving in the positive x direction (because it's -3t, not +3t). So, if the wave is moving right, that means the specified point can only be moving UP (the crest would be moving towards the specified point, so the particle must be moving up). Therefore, the answer is "c", the particle's instantaneous velocity is in the positive y-direction.
For the second one: Remember the equation velocity of string v=(T/linear mass density)^(1/2) ? Keep T constant. And, of course, frequency is pretty much always constant since frequency depends on the source!