The siren of a fire engine that is driving northward at 30.0 m/s emits a sound of frequency 2000 hz. a truck in front of this fire engine is moving northward at 20.0 m/s. what is the frequency of the siren's sound that the fire engine's driver hears reflected from the back of the truck? ,

As you are trying to move a heavy box of mass m, you realize that it is too heavy for you to lift by yourself. there is no one around to , so you attach an ideal pulley to the box and a massless rope to the ceiling, which you wrap around the pulley. you pull up on the rope to lift the box. use g for the magnitude of the acceleration due to gravity and neglect friction forces. once you have pulled hard enough to start the box moving upward, what is the magnitude f of the upward force you must apply to the rope to start raising the box with constant velocity? express the magnitude of the force in terms of m, the mass of the box.

Which of the following are guidelines to follow for obtaining accurate observations

Earth's atmosphere is composed of mostly two gases. name the two gases that make up the majority of the atmosphere and use the pie chart to tell the percentages of each.