As the army approached the bridge into the city, the commander told them to break step. he did not want the soldiers to march in cadence. why did the commander give this order? a) their rhythmic marching might resonate through the bridge and start the bridge swaying. b) rhythmic marching sends vibrations down into the water and sound travels fastest in water. c) marching in cadence causes the vibrations to travel faster through the air and reach the town faster. d) rhythmic sounds are amplified in comparison to non-rhythmic sounds; the towns people would hear them coming.

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.