Two people are singing a note at exactly 300 Hz. A microphone is placed in front of them to record their voices but when the track is played back, the recorded note is much quieter than the singers were producing. What is the best explanation for this result?

Shy diving is the only sport which doesnot require a high level of physical fitness

You need to be more specific.  i really don't know what a "motion map" is.you can draw a graph of an object's position, distance, displacement, speed,velocity, or acceleration versus time, or you can draw a graph of the object's x-position versus its y-position and not give any information about time at all.if the graph presents position or displacement against time,  then constant velocity is a straight line . . i.e. a line that has  constant slope.if the graph shows speed against time, then constant velocityis a horizontal piece of line.if the graph shows acceleration against time, then constant  velocity is a piece of line that lies on the x-axis . . it's value is zero. 

The density of the block of iron is lees than the density of mercury but the density of the block of iron is greater than the density of water