When 150 joules of work is done on a system by an external force of 15 newtons in 20. seconds, the total energy of that system increases by. (1) 1.5 × 102 J
(2) 2.0 × 102 J
(3) 3.0 × 102 J
(4) 2.3 × 103 J

Please include an explanation

Which of the following conditions lead you to see an absorption line spectrum from a cloud of gas in interstellar space? the cloud is extremely hot. the cloud is visible primarily because it reflects light from nearby stars. the cloud is cool and lies between you and a hot star. the cloud is cool and very dense, so that you cannot see any objects that lie behind it.