The Doppler effect is an effect produced by a moving source of sound or electromagnetic waves due to the relative motion of a source or a receiver. If an emergency vehicle approaches Bob and moves away from Jill, how does the frequency of the siren change?

A) Neither Bob or Jill perceive any change in the frequency of the siren.
B) As an emergency vehicle approaches Bob the frequency appears to increase.
C) As an emergency vehicle moves away from Jill the frequency appears to increase.
D) Bob does not notice any change until the vehicle passes him and the siren increases.

Mass (kg) force (n) 5 25 10 50 15 75 20 100 a student was trying to find the relationship between mass and force. he placed four different masses on a table and pulled them using a spring scale. the table shows the different masses used in the experiment and the force required to pull each mass. the student concluded that more force was required to pull heavier objects. what comment would you make regarding his conclusion? a) no clear relation can be observed between mass and force from the data. b) there is a direct proportion between the mass and force listed in the table. c) gravity should have been taken into account while performing the experiment. d) there is an inverse proportion between the mass and force listed in the table.

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Two resistors r1 and r2 may be connected either in series or parallel across an ideal battery with emf ε. we desire the rate of energy dissipation of the parallel combination to be 8.75 times that of the series combination. if r1 = 105 ω, what are the (a) smaller and (b) larger of the two values of r2 that result in that dissipation rate?