4. light travels at 3.0 % 10% m/s. how
* many seconds go by from the moment
the starter's pistol is shot until the smoke
is seen by the track timer 100 m away?

Ithink it is a. but i'm not 100 percent sure.

Distance covered = speed x timethe distance traveled going against the stream = distance traveled with the stream.therefore it is the speed and the time that are the variables.as he travels the same distance both ways, speed x time is the same for each way.going upstream his speed is 4 kph; going downstream his speed is 6 kph.therefore we have two simultaneous equations: time upstream x 4 = time downstream x 6time upstream + time downstream = 60 minutestherefore we have the equation: time upstream = 6/10 hour, time downstream therefore = 4/10 hour.distance traveled at 4km/hr in 6/10 hour = 24/10 = 2.4km.check: distance traveled at 6km/hr in 4/10 hour = 24/10 = 2.4km.

Ithink the answer for this is: an electromagnet is a magnet  with a soft metal core.

Answer4 million;