7) batteries properties battery brand average life cost a 12 hours $0.50 b 18 hours $2.00 c 24 hours $3.50 if a battery is needed for a smoke detector where the biggest priority is for the device to last as long as possible, then which brand is the best choice? a) battery a b) battery b c) battery c d) all 3 brands are equally good choices.

Without caring the cost of battery then battery C last the longest for average of 24 hrs. but if we include the cost, then we should calculate the cost per hour.

A.    $ 0.5 / 12 hrs = $ 0.042 per hr

B.    $ 2 / 18 hrs = $ 0.11 per hr

C.    $3.50 / 24 hrs = $ 0.15 per hrs

So the cheapest is battery A

sonar - device which is used to find the submit submarines, sankalp ship. sonar waves consists of a transmitter and detector which are installed in the observation centre on board of a ship. the ultrasonic waves are sent into the sea at high frequency about 1000 khz in all direction.

(75°f − 32) × 5/9 = 23.889°c