Because the hamburger is still hot from the grill, the cheese melts because of that heat.
The rate of acceleration of the crate would be 1 m/s^2 because the equation for force is F=ma and when you plug in your numbers you get 10=10a so a=1
Beat frequency, fb = |f2-f1|
That is, beat frequency is the absolute difference between two frequencies. Is is as a results of destructive and constructive inferences.
Therefore, in this case:
fb = 203 - 199 = 4 Hz