A special device can transmit sound out of phase from a noisy jackhammer to its op- erator using earphones. over the noise of the jackhammer, the operator can easily hear your voice while you are unable to hear his. why?1. these devices reduce jackhammer noise by using destructive interference to cancel the noisy sound, so he can hear your voice clearly.2. the operator's earphones are connected to your microphone, so he can hear your voice clearly.3. the operator's earphonex amplifies your voice, so he can hear your voice clearly.4. the operator's earphones change the fre- quencies of your voice, so he can hear your voice clearly.

Abox is sliding on a frictionless surface when it suddenly begins to rain heavily. if the downpour of rainfall falls vertically into the box

Why do some scientists and archeologists think that volta was not the first person to build a battery

Lake happy times contains 100 km3 of pure water. it is fed by a river at a rate of 50 km3/yr. at time zero, there is a factory on one shore of lake happy times that begins introducing a pollutant to the lake at a rate of 2km3/yr. there is another river that is fed by lake happy times at a rate that keeps the volume of lake happy times constant. this means that the rate of flow from lake happy times into the outlet river is 52km3/yr. in turn, the flow from this outlet river goes into another lake, lake sad times, at an equal rate. finally, there is an outlet river from lake sad times flowing at a rate that keeps the volume of lake sad times at a constant 100 km3 . (a) find the amount of pollutant in lake sad times at the end of 3 months. (b) at the end of 3 months, observers close the factory due to environmental concerns and no further pollu- tant enters lake happy times. how long will it take for the pollutant in lake sad times (found in part (a)) to be cut in half?