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as we know that the velocity vectors are at right angles
magnitude = ?
hypotenuse of a right
triangle.
v^2 = 90^2 + 4^2
v^2 = 8116
Taking the square root of both sides here we get,
v = 90.1 m/s
hope it helps
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mediums only, mechanical waves always propagate through medium
B south because north polarities line up with the opposite polarities