Explain why pluto has been re-categorized as a dwarf planet.

Explanation:

According to International Astronomical union a planet must satisfy the following three conditions-

1. It should orbit around sun(parent star).

2. It should have enough gravity to maintain almost spherical shape.

3. It should have cleared its neighbourhood around its orbit.

Pluto does not fulfill the third criteria and hence it has been re-categorized as dwarf planet.

work: w = fd (given)

work done by chet   =50*1 = 50 j

work done by mika =40*2 = 80 j

work done by sara =30*1.5 = 45 j

work done by bill =60*0.5 = 30 j

students in order from the greatest amount of work done to the least is mika> chet> sara> bill

hence option (b) is correct.

the duration of a photographic flash is related to an rc time constant, which is 0.100 μs for a certain camera.