Answer:a
Explanation:
We have to lift the load two loads up one story, so energy required is
let m be the mass of each load and h is the height of each story
Energy 
Here energy gained is the potential energy which depends upon the datum(floor).
For lifting one load up one story
Energy required
thus 
is half of 
So option a is correct
Answer:
1.327363 m/s
0.00090243 m
Explanation:
u = Initial velocity
v = Final velocity
m = Mass of flea
Energy
The velocity of the flea when leaving the ground is 1.327363 m/s
The flea will travel 0.00090243 m upward
Answer:
Scientists have studied eclipses since ancient times. Aristotle observed that the Earth's shadow has a circular shape as it moves across the moon. He posited that this must mean the Earth was round. Another Greek astronomer named Aristarchus used a lunar eclipse to estimate the distance of the Moon and Sun from Earth
