the minimum flying speee for a bird called a house martin is 9.0ms^-1. it reaches this speed by falling from its nest before swooping away. calculate the minimum distance its nest must be away above the ground.

The nest must be about  4.15 meters above ground

Explanation:

Use the velocity equation under accelerated motion (acceleration of gravity ):

which for this case has initial velocity = 0 (falls from the nest), final velocity = 9 m/s, and a = 9.8 m/s^2, then we can find the time needed in air while falling to reach the required speed:

We now use this time value to find the distance covered in free fall during 0.92 seconds:

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.