Chapter 13 - Worked Solutions
to selected extension questions from the OUP text Senior Physics -
Concepts in Context by Walding,
Rapkins and Rossiter
The sound that is reflected from the stand has to travel 300 m further then the other sound.
v = d/t = 300m /0.9 s = 333 m s-1
In general: L =
nl/4, where n = 1, 2, 3,
4, 5, .......
Sound is reflected from the fish and from the bottom.
Since the sound has traveled to the fish (and bottom) and back. It took 0.1 s to reach the fish and 0.125 s to reach the bottom. That is the sound took 0.025 s to travel from the fish to the bottom.
v = d/t
d = v.t
= 1450 x .025 = 36.25 m
the fish are 36 m from the bottom.
Points A, B, C, are points on the spring and therefore are moving outwards or inwards.
When the wave has gone 1 m further on point A is the same distance form the equilibrium.
Point B will have moved up to about the position o the 18 cm mark - a change of 38 cm.
Point c has moved soen to the -40 cm mark - a change of about -20 cm .
Therefore B has moved the greatest distance in the same time and therefore has the greatest velocity.
The velocity of the wave is 5 m s-1 and therefore goes 1 m in 0.2 of a second. When the wave has gone 1 m, C has moved down 20 cm.
Speed = distance / time = 20 cm/0.2 s = 100 cm s-1 = 1 m s-1.
Points have to instantaneously change direction.
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